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Machine tool guide rail error

The guide rail is the datum to determine the relative position relationship of each machine tool component on the machine tool, and it is also the datum of the machine tool movement. The accuracy requirements of lathe guide rail mainly include the following three aspects: straightness in horizontal plane; straightness in vertical plane; parallelism (distortion) of front and rear guide rails.

Straightness error of horizontal lathe guide rail

Influence of straightness error in vertical plane of horizontal lathe guide rail on machining accuracy

In addition to the manufacturing error of the guide rail itself, the uneven wear and installation quality of the guide rail are also important factors causing the error of the guide rail. The wear of guide rail is one of the main reasons for the decline of machine tool precision.

Drive chain error

The relative error between the two ends of the transmission chain refers to the error between the two ends of the transmission chain. It is generally measured by the angle error of the end components of the transmission chain.

The spindle rotation error refers to the variation of the actual rotation axis relative to its average rotation axis at each moment. It can be divided into three basic forms: radial circular run out, axial movement and angle swing.

The main reasons for the radial rotation error of the main shaft are: the coaxiality error of several sections of the spindle journal, various errors of the bearing itself, the coaxiality error between the bearings, and the winding degree of the main shaft. However, their influence on the radial rotation accuracy of the spindle varies with different machining methods.

The main reason for the axial movement is the Perpendicularity Error of the spindle shoulder end face and bearing bearing end face to the spindle rotation axis.

Different machining methods lead to different machining errors caused by spindle rotation error. When machining outer circle and inner hole on lathe, the radial rotation error of spindle can cause roundness and cylindricity error of workpiece, but it has no direct effect on the end face of workpiece. The axial rotation error of the spindle has little effect on the machining of outer circle and inner hole, but has great influence on the perpendicularity and flatness of the machined end face. In the process of thread turning, the rotation error of the main axis can make the lead of the processed thread produce periodic error.

The rotation accuracy of machine tool spindle can be improved by properly improving the manufacturing accuracy of spindle and box, selecting high-precision bearings, improving the assembly accuracy of spindle components, balancing high-speed spindle components, and preloading rolling bearings.

Factors of mould water mark

What are the causes of water mark and how to improve it? For example, U-shaped parts

Water mark is also called water line, which is the melting line caused by the combination of two strands of plastic injection flow.

The reasons are: the nozzle design position is not correct or the nozzle design is not good. Poor die exhaust, etc

During injection molding, the mold temperature is too low, the material temperature is too low, and the pressure is too small.

improve:

In the structure, the bone position is added at the place where the water line is easy to be generated. The short side of the U-shaped part should be designed to be consistent with the flow direction of the nozzle.
Improve the nozzle.
Improve beer and plastic.

Please list the operation process of mobile phone assembly

Mobile phone assembly process:

The auxiliary material is usually beer plastic factory first installed on the rubber shell, PCB is generally a whole board.

PCB to a shell: button assembly on case a – PCB board – Case B (screw) – battery cover – Test – package

PCB to B shell: fix the PCB on the B shell and limit the position – install the button on the upper limit of the a-shell – screw AB shell – install the battery cover – Test – package

Please draw the size chain of the whole mobile phone

Take the straight plate machine as an example, there is no decoration on the surface, and the thickness is based on the battery: the figure will not be drawn, but the thickness distribution will be discussed. A shell glue thickness 1.0 + LCD foam 0.30 + PCB board thickness (whole board, not to mention the thickness) + battery and battery cover clearance 0.15 + battery cover thickness 1.0

P + R keyboard matching profile

Take P + R + steel plate button as an example: the figure will not be drawn. Let’s talk about the thickness distribution.

The distance between dome sheet and conductive base is 0.05 + the height of conductive base is 0.30 + the thickness of silica gel body is 0.30 + the thickness of steel sheet is 0.20 + the distance between steel sheet and a shell is 0.05 + the adhesive thickness of a shell is 1.0 + the key cap is generally 0.50 higher than the surface of a shell

What should be paid attention to in the design and assembly of steel keys

Attention should be paid to the design of steel keys

The steel sheet should not be too thick, about 0.20, or the handle is too poor.
The steel sheet cannot transmit light, and the light can only pass through silica gel.
The steel sheet is required to be positioned, and the steel sheet is fixed on the a shell on the long bending wall.
The steel sheet shall be grounded.

What should be paid attention to in the design and assembly of PC keys

Attention should be paid to the design of PC key:

The PC chip should not be too thick, about 0.40, or it will feel too bad. It can’t be too thin, or it’s very soft, causing poor hand feeling.
The light transmission of PC is not limited, and radium carving can be done at the light transmission place.
If the surface of PC chip is to be cut, the slot width shall not be less than 0.80, and the sharp corner shall be rounded (r0.30).
The assembly is generally connected with PCB by pasting double-sided adhesive tape on the back of silica gel, or long positioning column on a shell, and positioning hole is opened on silica gel to limit and assemble on a shell.

What should be paid attention to in the design and assembly of PMMA keys;

The design requirement is the same as that of PC. Generally, the surface of PMMA sheet should be hardened.

What should be paid attention to in the design of metal shell

When the metal shell is disassembled, it is generally 0.05mm lower than the large surface and 0.05mm lower in the Z direction.

Metal requires grounding, grounding generally with conductive foam, conductive cloth, spring, etc.

When the metal parts are buckled, the amount of fastening should not be too large, generally about 0.30.

When screw holes are made on metal parts, bottom holes shall be made first and then mechanical tapping shall be carried out.

The influence of process selection on ESD test?

Generally speaking, if there are hardware on the surface, poor grounding will affect ESD test.

If there are electroplated decorative parts on the surface, ESD test will be affected.

mechanical polishing

1、 Mechanical polishing on the surface of aluminum products:

Mechanical polishing process is: rough grinding, fine grinding, polishing, polishing, sandblasting, brushing or rolling, etc., according to the roughness of the surface to take different procedures.

2、 Chemical oil removal: formula and process conditions of chemical oil removal liquid:

Formula: sodium hydroxide 30-50g / L, industrial detergent 0.5-1ml / L, water 70-125g.
Process conditions: temperature: 50-60 ℃, time: 1-2min
Rinse with water after degreasing.
Chemical removal of oxide film: acid pickling is carried out to neutralize the residual alkali solution on the surface of the product, and the natural oxide film is removed to expose the aluminum and aluminum alloy matrix of the product. For the production of aluminum alloy containing silicon, the mixed solution must be used for acid pickling to remove the dark silicon floating ash on the surface.

Formula of pickling solution:

Concentrated nitrate solution 200 ~ 270ml / L

Temperature: room temperature time: 1-3min

The formula of pickling solution for removing oxide film and silica fume on the surface of aluminum alloy products containing silicon is as follows

3 volume of concentrated nitric acid and 1 volume of concentrated hydrofluoric acid.

Temperature: room temperature time: 5-15min

After chemical pickling, aluminum and aluminum alloy parts must be cleaned immediately with flowing warm water and cold water to remove residual acid, and then immersed in water for chemical polishing.

CNC cutting machine

At present, in the normal work of the CNC cutting machine used in the factory, the operator can successfully complete the cutting work by using the breakpoint continuous cutting function of the cutting machine. The method is as follows: when the operator wants to stop the work and save the breakpoint of the cutting site in the process of cutting, press the s key to stop when running to the idle section, and then press the Enter key to exit the cutting operation. At this time, the breakpoint data is memorized by the system. At this time, the operator should remember the coordinate values in X and Y directions, and then turn to the idle path operation to make the cutter move in the opposite direction until the coordinate values in X and Y directions are the same as the coordinate values memorized above, and the positive and negative signs are different (this position is the starting point of the program and also the origin of the steel plate). Next time when starting the machine, enter the letter C at the corner of the steel plate to continue to complete the last interrupted cutting operation.

According to the above operation method, the operator must first control the cutter to return to the starting point of the program (or the origin of the steel plate) in order to continue cutting in the next work. Obviously, if the cutting machine breaks down suddenly in normal operation (such as power failure, servo system failure, control computer crash, etc.), the operator cannot make it return to the starting point of the program (or the origin of the steel plate) because it has no power-off memory function.

In this case, our general practice is: after the cutting machine is repaired and restored to normal, the remaining steel plate is aligned, and then a new program is compiled by the programmer for cutting. In this way, some parts at the breakpoint are not cut completely, which makes them unable to be used, resulting in the waste of raw materials, increasing the production cost, and also bringing repetitive labor to the programmer, which leads to the reduction of production efficiency.

In the production practice, we successfully solve the problem of returning to the program starting point (or steel plate origin) after the cutting machine failure occurs by setting the zero point artificially. The specific operation method is as follows: first, operate the cutting machine to make the longitudinal sliding seat contact the measuring rod slowly, and compress the spring to make it deform properly. At this time, set the dial indicator head to “0”; then use the same method to set the dial indicator head of another zero setting device to “0”. No matter how many X and Y coordinates are displayed by the cutting machine, press Z key to make them all return to zero. This position is the zero point set by human for the cutting machine. Then operate the cutting machine according to the position of the steel plate to set the starting point of the program (or the origin of the steel plate). After setting, remember the coordinates of X and Y directions at this time. This coordinate value is the relative position between the zero point of the cutting machine and the starting point of the program (or the origin of the steel plate). When the fault occurs, first remove the fault, after the cutting machine returns to normal, use the above method to make it zero, and then use the coordinate value remembered to find the starting point of the program (or the origin of the steel plate). In this way, the breakpoint continuous cutting can be realized smoothly until the whole steel plate is cut.

Micro system EDM machining technology

In the field of microsystem technology, product development needs the common development of a variety of micro technologies. For example, it requires the joint efforts of micro mechanical parts, micro optical parts and micro electronic components. Micro digital cameras need the cooperation of the above micro technologies. The increase of product demand in the field of micro technology also leads to the increase of demand for micro machinery products, which puts forward higher requirements for the production and processing of mechanical products. Therefore, the production technology of micro products, the production and manufacturing of micro structural parts and the research and development of micro components are new areas that need to be strengthened urgently.

Because of the limited machinability, high precision and small manufacturing tolerance, the machining of high hardness micro parts is a very difficult task. In the industrial mass production, the main production process of micro structural parts is rolling, micro die casting, hot stamping and so on. In addition to grinding and laser cutting, EDM is also a feasible processing technology for micro structure parts with high wear resistance. Due to the corrosion characteristics of the electrode in micro machining system, EDM is widely used in micro parts. These two processing methods have nothing to do with the properties of the workpiece material, are not affected by the workpiece material, and almost do not produce cutting force, so they can produce very small structural parts.

The concept of micro EDM corrosion machining (abbreviated as μ – EDM) refers to the production and processing of micro workpieces and micro structural parts by means of EDM. It is an application of EDM in the field of micro machining in mechanical machining. In micro EDM, the contour size of the workpiece is obviously less than 1 mm. The difference between micro EDM and traditional EDM is first of all very small electrode. In addition, it is the electrical parameters and production process parameters suitable for micro workpiece and micro structural parts. Due to the small volume and size of the micro workpiece, all processing parameters can not exceed the limit of the thermal load of the workpiece. This means: to reduce the discharge energy, reduce the current density.

In addition to the standard motor with adjustable current, the modern EDM equipment is equipped with a relaxation oscillator, which can be used for micro EDM and surface precision machining. According to the discharge capacitance and distributed capacitance of the electrical conduction distance, the capacitive micro oscillator can generate very small discharge energy. 1 μ J / each discharge process; the minimum operating current is 0.1A; the shortest discharge duration is 50ns; and the discharge frequency reaches 10MHz. The minimum distance of spark can reach 15 μ M. At present, the minimum structure size that can be achieved by micro EDM is about 20 μ M. Japanese researchers have successfully machined holes with a diameter of 5 μ m on a steel sheet with a thickness of 10 μ M. When machining this kind of hole, they fully control the discharge capacitance of electrical wire and fixture system in the process of electric spark corrosion, making it less than 10PF. In micro EDM corrosion machining, the machine tool is only allowed to have very small discharge capacitance, such as using ceramic clamps and shielded electrical wires to reduce the discharge capacitance of the machine tool system; capacitors and circuit boards should also be strictly separated from the processing electrode in space.

Tool path generation method

The following is a brief introduction to the tool path generation method. NC tool path generation method for lines, surfaces and volumes

The technology started from 2D drawing, experienced the development stage of 3D wireframe, surface and solid modeling, and has been to the parametric feature modeling. NC machining is mainly driven by points and lines, such as hole processing, contour processing, plane area processing and so on. This kind of processing requires high level of operator and complex interaction. In the development stage of surface and solid modeling, solid based machining appears. The machining object of solid machining is an entity (generally represented by CSG and B-rep), which is obtained by some basic voxels through set operation (Union, intersection and difference operation). Solid machining can be used not only for rough machining and semi finishing machining of parts, but also for the research and development of feature-based NC programming system, which is the basis of feature-based machining.

Feature based NC tool path generation method

Parametric feature modeling has a certain period of development, but the research on Feature-based tool path generation method is just beginning. Feature processing makes NC programmers not to operate the low-level geometric information, but to directly carry out NC programming for the features that meet the habits of engineering and technical personnel, which greatly improves the programming efficiency.

W. In their research, r.mail and a.j.mcleod proposed a feature-based NC code generation subsystem. The working principle of this system is that each machining process of a part can be regarded as the sum of the machining of the shape feature group of the part. Then the whole shape feature or shape feature group is processed separately, then the part is finished. The NC code of each shape feature or shape feature group can be generated automatically. The developed system is only suitable for 2.5D parts processing.

Lee and Chang developed a tool path generation system for convex free-form surfaces by using virtual boundary method. The working principle of this system is that a minimum rectangle block is embedded in the convex free-form surface, so that the convex free-form surface feature is converted into a concave feature. The combination of the smallest rectangle and the final product model constitutes an indirect product model called virtual model. The tool path generation method is divided into three steps: (1) cutting polyhedron feature; (2) cutting freeform surface feature; (3) cutting intersection feature.

The basis of feature processing is solid processing, which can also be considered as higher-level entity processing. However, feature processing is different from solid processing, which has its own limitations. There are several differences between feature processing and solid machining

In concept, feature is the functional element of a part, which conforms to the operating habits of engineering and technical personnel and is well known by engineering and technical personnel; entity is a low-level geometric object, a geometric body obtained through a series of Boolean operations, without any functional semantic information; entity processing is often a one-time processing of the whole part (entity). But in fact, a part is not likely to be processed with only one knife at a time. It often needs to go through a series of steps such as rough machining, semi finishing and finishing. Different parts of parts are generally processed with different cutters; sometimes a part needs to be turned and milled. Therefore, solid machining is mainly used for rough machining and semi finishing of parts. Feature processing solves the above problems in essence, and feature processing has more intelligence. Certain fixed processing methods can be specified for specific features, especially those already specified in the step standard. If we have developed a specific processing method for all the standard features, we can imagine the convenience of machining those parts which are made up of standard features. If CAPP system can provide corresponding process characteristics, NCP system can greatly reduce interactive input and have more intelligence. However, these solid machining can not be realized; feature processing is helpful to lay a good foundation for the realization of CAD, CAPP, CIMS and even Concurrent Engineering (CE), while entity machining is powerless to these

High precision characteristics of computer gongs

From the development of precision machining to ultra precision machining, is the development direction of the world’s industrial powers. Its precision ranges from micron level to submicron level and even nanometer level (< 10nm).

At present, under the requirement of high machining precision, the machining accuracy of ordinary computer gongs has been increased from ± 10 μ m to ± 5 μ m; the machining accuracy of precision machining center has been increased from ± 3 ~ 5 μ m to ± 1 ~ 1.5 μ m, or even higher; the ultra precision machining accuracy has entered the nano level (0.001 μ m), the spindle rotation accuracy is required to reach 0.01 ~ 0.05 μ m, the roundness is 0.1 μ m, and the surface is machined Roughness Ra = 0.003 μ m, etc. These machine tools generally adopt vector control variable frequency drive motorized spindle (motor and spindle integration), the spindle radial runout is less than 2 μ m, the axial movement is less than 1 μ m, and the shafting imbalance reaches g0.4 level.

There are mainly two types of feed drive of high-speed and high-precision machining machine tools: “rotary servo motor plus precision high-speed ball screw” and “direct drive of linear motor”. In addition, the new parallel machine tool is also easy to realize high-speed feed.

Due to its mature technology and wide application, ball screw not only has a high precision (ISO 3408 grade 1), but also has a relatively low cost to realize high-speed, so it is still used by many high-speed machine tools. The current high-speed machining machine driven by ball screw has a maximum moving speed of 90m / min and an acceleration of 1.5g.

Ball screw belongs to mechanical transmission. In the transmission process, there are inevitably elastic deformation, friction and reverse clearance, which will cause motion lag and other nonlinear errors. In order to eliminate the influence of these errors on machining accuracy, linear motor direct drive was applied to machine tools in 1993. Because of the “zero transmission” without intermediate link, it has small inertia and rigid system High speed and acceleration can be achieved with high speed and fast response, and the stroke length is not limited theoretically. The positioning accuracy can also reach a higher level under the action of high-precision position feedback system. It is an ideal driving mode for high-speed and high-precision machining machine tools, especially for medium and large-scale machine tools. At present, the maximum moving speed of high-speed and high-precision machining machine tools using linear motor has reached 208 M / min and the acceleration is 2G, and there is still room for development.

CNC machine tool coordinate system

When determining the coordinate axis of CNC machine tool, the Z axis is generally determined first, and then the X axis and Y axis are determined.

(1) Z axis. The axis parallel to CNC machine tool spindle (transmitting cutting power) is regarded as z-axis, and the direction of tool away from workpiece is the positive direction of z-axis. For CNC machine tools with spindle, such as horizontal lathe and vertical lifting table milling machine, the spindle axis of CNC machine tool is taken as Z axis; for CNC machine tools without spindle, such as shaper, the coordinate axis perpendicular to the clamping surface is specified as Z axis. For CNC machine tools with several spindles, such as gantry milling machine, one of the main spindles perpendicular to the worktable surface is selected as the main spindle, and the z-axis direction is determined by it.

(2) X axis. The x-axis is located in the horizontal plane, perpendicular to the Z-axis and parallel to the workpiece clamping surface. For CNC machine tools with workpiece rotation, such as lathe, the X axis is in the radial direction of the workpiece and parallel to the horizontal carriage, and the direction of the cutter leaving the workpiece rotation center is the positive direction of the X axis. For CNC machine tools with tool rotation: if z-axis is horizontal, such as horizontal milling machine, boring machine, etc., the positive direction of x-axis points to the right when viewed from the back end of the tool (spindle) to the workpiece. If the z-axis is vertical, such as vertical milling machine, drilling machine, etc., the positive direction of x-axis points to the right when looking at the column when facing the cutter (spindle). For CNC machine tools without spindle: such as planer, the main cutting direction is x axis.

(3) Y axis. The y-axis direction is determined according to the selected Z and X axes according to the Cartesian coordinate system of right-hand right angle.

(4) Steering of a, B and C. After selecting the X, y and Z axes, the positive rotation directions of a, B and C are determined according to the right hand helix rule.

(5) Additional coordinates. If the CNC machine tool is outside the basic rectangular coordinate system X, y, Z, and other axes are parallel to their coordinate system, the additional rectangular coordinate system is designated as u, V, W and P, Q, R.

Computer gong processing machine tool guide

The guide rail of machine tool is mostly made of steel or cast iron. If this kind of guide rail is scratched, it should be repaired, otherwise it will enlarge the scratch and even affect the use of machine tool. In the long-term use of machine tool guide rail and other friction pairs, due to the different degree of friction between the two contact surfaces, the friction pair surface has different degrees of wear, which seriously affects the machining accuracy and production efficiency of the machine tool. The repair of machine tools and other worn parts usually adopts the methods of inlaying or replacing metal plates and polymer materials, which not only requires a large number of accurate processing and manufacturing, but also often requires manual scraping and grinding of the machined surface. There are many repair procedures and a long construction period.

Solution: using the international advanced polymer 2211f metal repair material to repair the scratch of the guide rail of the gantry milling machine, the scratch part of the guide rail can be repaired in a few hours and put into use. Practice shows that this method is simple, time-saving, good repair quality and low cost. With its unique adhesion, excellent compressive strength, oil resistance and wear resistance, it can provide a long-term protective layer for components, effectively solve the problems that cannot be solved by traditional maintenance methods for large-scale equipment that can not be disassembled. The performance of the equipment is improved, the fit clearance of parts is improved, and the normal operation of production is guaranteed to the maximum extent It saves a lot of time and money, and provides a long-term good guarantee for the normal operation of enterprise equipment.

Repair Principle: polymer composite material is a kind of composite material, which is made of polymer, metal or ceramic superfine powder, fiber, etc. under the action of curing agent and curing accelerator. All kinds of materials draw on each other’s strong points and complement each other in performance, resulting in synergistic effect, so that the comprehensive performance of the composite is better than that of the raw materials. Because of its strong adhesion, mechanical properties and chemical corrosion resistance, it is widely used in the repair of mechanical wear, scratch, pit, crack, leakage and casting sand hole of metal equipment, as well as the chemical anti-corrosion protection and repair of various chemical storage tanks, reaction tanks and pipelines.

Repair process:

Burn the scratched part with oxygen acetylene flame (control the temperature, avoid surface annealing), and bake the oil on the surface of permeating metal all the year round until there is no spark.
The scratched part shall be treated with angle grinder, the grinding depth shall be more than 1 mm, and the groove shall be polished along the guide rail, preferably dovetail groove (as shown in the figure). The scratch on both ends of the hole is deepened to change the stress condition.
Clean the surface with absorbent cotton dipped in acetone or absolute ethanol.
Apply the mixed and uniform 2211f to the scratched surface; the first layer should be thin and evenly covered with the scratch surface to ensure the best bonding between the material and the metal surface. Then, apply the material to the whole repair part and press repeatedly to ensure that the material is filled and reaches the required thickness, which is slightly higher than the rail surface.
It takes 24 hours for the material to reach all properties at 24oc. In order to save time, the temperature can be increased by halogen lamp. The curing time will be shortened by half when the temperature is increased by 11oc. The best curing temperature is 70oC.
After the material is solidified, the material higher than the surface of guide rail shall be repaired and leveled with fine grindstone or scraper, and the construction is completed.

Computer gong processing – plane grinder

As an important processing method of precision factory, the plane grinder must formulate strict process specification. Strict and standard operation can ensure the stable precision and quality of the processed parts.

first, you must be familiar with the operation of the plane grinder and understand the performance of the plane grinder.
before starting the machine, wear protective glasses and work clothes, fasten clothes and sleeves, and put long hair plate into the working cap. Do not wear scarves or gloves to operate the grinder.
before operation, tools, measuring tools and workpieces shall be placed in order to remove any sundries that hinder the operation and operation of the equipment. Before operation, check whether the safety shield of transmission part is complete and fixed, and handle the abnormal of plane grinder in time.
before starting, check whether the transmission part and operating handle of the plane grinder are normal and sensitive, and see whether the lubricating oil system of each part is smooth and whether the electronic ruler displays data.
before starting the machine, adjust the limit block of the left and right impact blocks according to the grinding length of the workpiece and lock it tightly.
the grinding wheel must be installed in static balance, and it should be balanced again after correction. The diamond of the grinding wheel dresser must be sharp, and the height of the point should be consistent with the horizontal plane of the center line of the grinding wheel. It is forbidden to use the blunt diamond to trim the grinding wheel. When finishing, the dust collector must be started.
start the spindle of grinding machine to idle for 1 to 2 minutes, observe the operation, pay attention to the height of the grinding wheel about 5 cm from the table surface; confirm that the lubrication and cooling system is smooth and all parts are running normally before grinding.
check the workpiece, load and unload the grinding wheel and handle the machine tool fault, and then stop the grinding wheel after it is withdrawn from the workpiece.
it is not allowed to place non processed goods on the working face, workpiece and electromagnetic disc, and it is forbidden to knock or calibrate the workpiece on the working face and permanent magnet suction disk.
when moving the disk switch to mount the workpiece after adsorption, it must be checked firmly and then ground. When absorbing the higher or smaller workpiece, the proper height of the back plate shall be added to fix it to prevent the workpiece from loosening and causing potential accidents.
when the grinding wheel approaches the workpiece, it is necessary to touch the workpiece in a forbidden state to move away. If the grinding wheel does not leave the workpiece, it is not allowed to stop running. The grinding feed shall be small and large, and it shall not increase suddenly. The cutting shall be conducted evenly to prevent the grinding wheel from hitting the workpiece to break.
during operation, attention must be paid to the work, and nothing related to processing shall be done. After the grinding machine or the workpiece is finished, the table surface shall not be blown by air pressure to prevent dust from entering the track of the plane grinder to affect the hand feeling and accuracy. It is not allowed to allow others to operate the grinder without authorization or allow idle personnel to walk around the machine tool. Especially on the side of the grinder