Machinery industry – Page 34 – CNC Machining & Turning, Milling, Metal parts

Six basic problems to be considered in CNC machining

Generally, the workpiece processed by computer gongs has complex shape, many working procedures and many kinds of cutting tools. It is often necessary to complete the whole process from rough machining, semi finish machining to finish machining after one clamping. So the program is more complex. Consider the following when programming.

1. Carefully analyze the drawings and determine the reasonable process route.

2. The size and specification of the tool shall be selected, and the measured actual size shall be filled into the tool card.

3. Determine reasonable cutting parameters. It mainly includes spindle speed, back draft, feed speed, etc.

4. There should be enough space for automatic tool change to avoid collision with workpiece or fixture. It is recommended to set the tool change position at the machine origin.

5. In order to facilitate the inspection and debugging of the program, the processing contents of each step can be arranged in different subprograms, while the main program mainly completes the tool change and subroutine call. This procedure is simple and clear.

6. Check and test run the programmed program, and pay attention to whether there is interference between tools, clamps or workpieces. When checking the m, s and t functions, it can be carried out under the z-axis locking state.

Brief introduction of positioning and clamping of CNC machining center workpiece

（1） Selection of positioning datum for CNC machining center

(1) Try to select the design datum on the part as the positioning datum.

(2) One clamping can complete the processing of all key precision parts.

(3) When the machining center not only processes the datum but also completes the machining of each station, the selection of its positioning datum needs to consider completing as many machining contents as possible.

(4) When the positioning datum and design datum of the part are difficult to coincide, the assembly drawing shall be carefully analyzed to determine the design function of the design datum of the part. Through the calculation of the dimension chain, the tolerance range between the positioning datum and the design datum shall be strictly specified to ensure the machining accuracy.

（2） Selection and use of fixture in CNC machining center

(1) According to the characteristics of machine tools and machining needs of machining centers, the commonly used fixture types are special fixture, combined fixture, adjustable fixture, group fixture and workpiece unified benchmark positioning fixture system.

(2) The high flexibility of machining center requires that the fixture is more compact and simple than the general machine tool, the clamping action is more rapid and accurate, the auxiliary time is reduced as far as possible, the operation is more convenient, labor-saving and safe, and the sufficient rigidity and flexibility are ensured. Therefore, pneumatic and hydraulic clamping devices are often used.

(3) In order to keep the workpiece fully exposed to all the surfaces to be processed in this positioning and clamping, the clamp shall be as open as possible, and the space position of the clamping element shall be low or low, so there must be space for the tool movement path.

(4) Considering the minimum distance between the spindle and the worktable and the clamping length of the tool, the installation position of the fixture on the worktable of the machine tool shall ensure that the processing content of the workpiece can be completed within the range of the spindle travel.

(5) It is not allowed to interfere with fixture or workpiece during automatic tool change and worktable exchange.

(6) Sometimes, the positioning block on the fixture is used when installing the workpiece. In the process of processing, in order to meet the requirements of the processing of front and rear left and right stations and prevent interference, the workpiece can be removed after being clamped. Therefore, it is necessary to consider how to maintain the positioning accuracy of the workpiece after removing the positioning elements.

(7) Try not to change the clamping point in the middle of processing.

（3） CNC machining to determine the best position of parts on the machine tool table

What are the characteristics of CNC machining center

CNC machining center is a CNC machine tool with tool library and automatic tool change device, which has the comprehensive functions of CNC boring, milling and drilling machine.

CNC machining center has good processing consistency and economic benefits. Compared with other CNC machine tools, it has the following characteristics:

1. The processing of workpiece is complex and the process flow is very long. It can eliminate the human interference factors in the process flow and has high production efficiency and quality stability.

2. Because of the centralized working procedure and the automatic tool change device, the workpiece can complete the complex processing of milling, drilling, boring, expanding, reaming, tapping and so on with the accuracy requirements after one clamping.

3. When there is an automatic exchange worktable, when one workpiece is processed, the other worktable can realize the clamping of workpiece, thus greatly reducing the auxiliary time and improving the processing efficiency.

4. The larger the tool capacity, the wider the machining range, and the higher the flexibility program.

Precautions for wire cutting

1. Before starting the machine, check whether the electrical parts are loose. If there are broken wires and parts falling off, inform the professional personnel in time for maintenance.

2. Check the tension of molybdenum wire.

3. Check whether the guide wheel is damaged and change the position of the working face in time to prevent the molybdenum wire from being broken.

4. Check if there is a communication slot in the wire stopper, adjust the position of the working face in time to prevent the molybdenum wire from being broken.

5. Check that the lubricating part of the machine tool has enough lubricating oil.

6. Daily maintenance:

6.1. Add No.30 engine oil once per shift for transverse feed gearbox and longitudinal feed gearbox.

6.2. Each drive shaft, screw rod nut and guide plate of the screw storage barrel shall be added with 30 engine oil once for each plate.

Routine maintenance of CNC lathe

1. Clean and lubricate each guide rail surface every day. For machine tools with automatic lubrication system, regularly check and clean the automatic lubrication system, check the oil volume, add lubricating oil in time, and check whether the oil pump starts and stops regularly.

2. Check whether the automatic lubrication system of the spindle box works normally every day, and change the lubricating oil of the spindle box regularly.

3. Check whether the cooling fan in the electrical cabinet works normally, whether the air duct filter screen is blocked, and clean the dust.

4. Pay attention to check the cooling system, check the liquid level, add oil or water in time, and replace and clean the dirty oil or water.

5. Pay attention to check the main shaft drive belt and adjust the tightness.

6. Pay attention to check the tightness of guide rail insert strip and adjust the clearance.

7. Pay attention to check whether the oil pump in the oil tank of the hydraulic system of the machine tool has abnormal noise, whether the height of the working oil level is appropriate, whether the indication of the pressure gauge is normal, and whether the pipeline and all joints have > leakage.

8. Pay attention to check whether the guide rail and machine tool protective cover are complete and effective.

9. Pay attention to check the mechanical accuracy of all moving parts to reduce the deviation of shape and position.

10. Clean the machine tool, clean the iron scraps and wipe the cooling liquid at the guide rail every day after work to prevent the guide rail from rusting

Processing customized two-color plastic mold for daily necessities

Two color mold: two kinds of plastic materials are injected on the same injection molding machine, which are divided into two parts, but the product is only molded once. Generally, this kind of molding process is also called double material injection molding, which is usually completed by a set of molds and requires a special two-color injection molding machine. At present, the two-color mold is becoming more and more popular in the market. This process can make the appearance of the product more beautiful and easy to change colors without spraying, but the cost is expensive and the technical requirements are high.

1. The two shapes of the master mold are different, forming one product respectively, while the two shapes of the male mold are exactly the same.

2. After the front and back dies of the die rotate 180 o in the center, they must match. This inspection must be done in the design, which requires high positioning processing of the mold base.

3. The total thickness of front formwork panel plus a plate shall not be less than 170mm. Please carefully check other reference data of this type of injection molding machine, such as maximum mold thickness, minimum mold thickness, Ko hole distance, etc.

4. The nozzle of the three plate mold should be designed to automatically demould. Pay special attention to the demoulding action of the soft rubber nozzle.

5. When designing the master mold for the second injection molding, in order to avoid the second master mold inserting (or wiping) to damage the rubber position of the first molded product, part of the master mold can be designed to avoid air. However, the strength of each sealing position must be carefully considered, i.e. in injection molding, is there any possibility of plastic deformation under large injection pressure, leading to the possibility of batch front in the second injection molding?

6. During injection molding, the product size of the first injection molding can be slightly larger, so that it can be pressed more tightly with another male mold during the second molding, so as to achieve the sealing effect.

7. Pay attention to whether the flow of plastic will impulse the products that have been molded for the first time during the second injection molding, so as to deform the glue position? If this is possible, we must find ways to improve.

8. Before closing the A and B plates, pay attention to whether the front mold slider or inclined roof will reset first and crush the product? In this way, we must find a way to make the A and B plates close the mold first, and then the slider or inclined roof of the front mold can be reset.

9. The water transport layout of the two female and male formworks shall be as sufficient as possible, and shall be balanced and the same.

10.99% of the cases are that the hard part of the product is injected first, and then the soft part of the product is injected. Because soft rubber is easy to deform.

Introduction of two color mold