July 2019 – Page 10 – CNC Machining & Turning, Milling, Metal parts

Analysis of the Common Defects in Zinc Alloy Die Castings

Zinc alloy die castings are widely used in various decorative fields, such as furniture accessories, architectural decoration, bathroom accessories, lighting parts, toys, tie clips, belt buckles, bags, various metal decorative buckles, etc. Therefore, the surface quality of the castings is required to be high, and good surface treatment performance is required. The most common defect of zinc alloy die castings is surface blistering.

Defect characterization: There are protuberant bubbles on the surface of die castings, which are found after die casting, exposed after polishing or processing, and appearing after oil spraying or electroplating.

Causes:
1. Cavitation: mainly stomata and contraction mechanism, stomata are often round, and contraction is mostly irregular.

(1) Causes of pore formation: In the process of filling and solidification of liquid metal a, the gas intrusion leads to the formation of holes on the surface or inside of castings. B. Invasion of vaporized gas from paint. C alloy liquid contains too much gas and precipitates during solidification.

When the gas in the cavity, the volatile gas from the coating and the gas from the alloy solidification are not exhausted properly in the die, the air holes formed in the castings will be left at last.

(2) Causes of shrinkage: during the solidification of liquid metal, shrinkage occurs because of shrinkage of volume or lack of liquid metal feeding at the final solidification part. B. Local overheating of uneven thickness castings or castings results in slow solidification at a certain part and concave surface formation during volume shrinkage. Because of the existence of air holes and shrinkage holes, the holes may enter into water during surface treatment of die castings. When spraying paint and baking after electroplating, the gas in the holes will expand by heat; or the water in the holes will change into vapor and volume expansion, which will cause foaming on the surface of castings.

2. Intergranular corrosion causes:

Harmful impurities in zinc alloy composition: lead, cadmium and tin will gather at the grain boundary and lead to intergranular corrosion. Metal matrix will be broken by intergranular corrosion. Electroplating accelerates this disadvantage. The parts affected by intergranular corrosion will expand and the coating will be jacked up, resulting in foaming on the surface of castings. Especially in wet environment, intergranular corrosion will cause casting deformation, cracking, and even breakage.

3. Cracks: water marks, cold isolation marks and hot cracks.

Watermark and cold barrier: In the filling process of liquid metal, the contact wall of liquid metal first solidified too early, and then the liquid metal can not be fused with the solidified metal layer, forming overlapping lines at the butt of the casting surface, resulting in strip defects. Water marks are usually on the shallow surface of castings, while cold barrier marks may penetrate into the inner part of castings.

Hot crack: a when the thickness of the casting is uneven, the solidification process produces stress; B is premature ejection, metal strength is not enough; C is uneven ejection, D is too high die temperature to make the grain coarser; e is harmful impurities.

All the above factors may cause cracks.

When there are water marks, cold barrier lines and hot cracks in die castings, the solution will infiltrate into the cracks during electroplating, and turn into steam when baking, and the plating layer will be bubbled by air pressure.

Solutions to defects:

The key to control the production of gas holes is to reduce the amount of gas mixed into the casting. The ideal metal flow should be accelerated from the nozzle through the diversion cone and runner into the cavity to form a smooth and uniform metal flow. The conical runner design means that the flow should be gradually reduced from the nozzle to the inner runner, which can achieve this goal. In the filling system, the gas mixing is due to the mixing of turbulence and liquid metal to form pore. From the study of the simulation die casting process of liquid metal entering the cavity from the casting system, it is obvious that the sharp transition position and increasing cross-section area of the runner will cause turbulence and entrainment of the liquid metal flow. Only a smooth liquid metal can facilitate the gas entering the overflow slot from the runner and the cavity. And exhaust groove, discharge out of the die.

For shrinkage: to make all parts of the die casting solidification process as uniform as possible heat dissipation, and solidification at the same time. Shrinkage can be avoided by reasonable nozzle design, thickness and location of inner nozzle, die design, temperature control and cooling. For the phenomenon of intergranular corrosion, it is mainly to control the content of harmful impurities in alloy raw materials, especially lead < 0.003%. Pay attention to the impurities brought by waste.

For water marks and cold partition marks, the appearance of cold partition marks can be reduced by increasing the temperature of the die, increasing the speed of the inner gate, or increasing the overflow groove in the cold partition area.

For hot cracks: the thickness of die castings should not change sharply to reduce stress generation; the relevant die casting process parameters should be adjusted; and the die temperature should be lowered.

Application of Cast Iron Drainage Pipe

1. Vertical and horizontal drainage on the back and side ditches of various retaining walls of expressway;

2. Drainage of tunnels and underground tunnels;

3. Water supply and drainage of municipal works, water purification plants, sewage plants, garbage dumps, etc.

4. Drainage of golf courses, stadiums, parks and other recreational green spaces;

5. Developing slope soil and water conservation on hillside;

6. Underground drainage of land preparation works;

Cast iron drain pipe is suitable for pavement structure with waterproof layer. The lower end of the pipe should extend at least 0.15-0.20 m below the bottom of the lane board to prevent seepage on the rib surface of the main girder.

Common technical terms for metal stamping dies

What are the technical terms of stamping die?
1 blanking
It is a kind of stamping process that separates part of material or workpiece from other part of material, workpiece or waste by means of punching die. Punching is the general name of the separation processes of cutting, blanking, punching, punching, slotting, cutting, chipping, trimming, tongue cutting, cutting and dressing.
2 incision
It is a stamping process in which the material is partially rather than completely separated along the open contour. The material that is cut and separated is located on or basically on the plane before separation.
3 trimming
It is a kind of stamping process that uses the edge of the part in the process of trimming to make it have a certain diameter, a certain height or a certain shape.
4 cut tongue
It is a kind of stamping process that partially separates the material along the open contour rather than completely separates it. The partially separated material has a certain position required by the workpiece and is no longer located on the plane before the separation.
5 cut off
It is a stamping process that separates the material along the open contour, and the separated material becomes a workpiece or a working piece.
6 flaring
It is a kind of stamping process that expands the hollow or tubular parts outward in the open place.
7 punching
It is a stamping process that separates redundant materials from materials or working parts along the closed contour, and obtains the required holes in materials or working parts.
8 deficiency
It is a stamping process that separates redundant materials from materials or working parts along the open contour, and opens the contour to form a gap whose depth does not exceed the width.
9 flush tank
It is a stamping process that separates the redundant material from the material or work piece along the open contour. The open contour is grooved and its depth exceeds its width.
10 punching center hole
It is a kind of stamping process in which shallow concave central hole is formed on the surface of the working piece, and the back material has no corresponding bulge
11 fine blanking
It is a kind of smooth blanking. It uses a fine blanking die with a toothed blanking plate to make the whole section of the punch piece smooth.
12 progressive die
It is a die with two or more working positions. The material is fed into the die one by one with the stroke of the press, so that the stamping parts can be formed step by step.
13 single process Die
It is a die that only one working procedure is completed in one stroke of press.
14 combined die
It is a general adjustable complete set of punching dies for all kinds of punches according to geometric elements (straight line, angle, arc, hole). The outline of planar stamping parts usually needs several sets of combined stamping dies to be punched in stages.
15 pressure bump
It is a stamping process in which the punch is used to squeeze the material into the opposite pit to form a bulge.
16 embossing
It is a kind of stamping process in which shallow concave patterns, patterns, words or symbols are formed on the surface of workpiece by local forced extrusion. The back of the embossed surface does not correspond to a shallow bump.
17 forming
It is a general term for stamping process that depends on material flow and does not depend on material separation to change the shape and size of working parts.
18 smooth blanking
It is a blanking process that can directly obtain all or almost all of the whole section without renovation. Torsional bending is a stamping process in which one part of a flat or partial flat part is twisted at a certain angle relative to the other part.
19 roll edge
It is a stamping process that rolls the edge of the working piece into a closed circle. The axis of the curling circle is linear.
20 coiling edge
It is a stamping process to roll the upper edge of the hollow part into a closed circle.
21 drawing
It is a kind of stamping process to change the straight blank or workpiece into a curved surface. The curved surface is mainly formed by the extension of the material at the bottom of the punch.
22 stretch bending
It is a stamping process to realize bending deformation under the combined action of tension and bending moment, so that the whole bending cross-section is subjected to deep drawing stress.
23 bulging
It is a stamping process that expands hollow or tubular parts along the radial direction.
24 section cutting
It is a stamping process that divides the forming process into several parts.
25 school level
It is a stamping process to improve the flatness of parts.
26 undulating forming
It is a stamping process that relies on the extension of materials to form local depressions or bulges in the working parts. The change of material thickness in undulating forming is formed naturally in the process of deformation, not the requirement specified by design.
27 bending
It is a kind of stamping process that makes use of pressure to produce plastic deformation of material and then bend it into a shape with certain curvature and angle.
28 chisel
Cutting is a blanking or punching process using a cutting die with a sharp edge. Cutting does not have a punching die, but only a flat plate underlying the material. Most of the punched material is non-metal.
29 Deep Hole Punching

It is the punching process when the diameter of the hole is equal to or less than the thickness of the punched material.
30 blanking
A stamping process in which materials are separated along closed contours. The separated materials become workpieces or process parts, most of which are planar.
31 necking
It is a kind of stamping process to compress hollow or tubular openings to reduce them.
32 plastic surgery
It is a stamping process that relies on material flow and changes the shape and size of workpiece in a small amount to ensure the accuracy of workpiece.
33 refurbishment
It is a stamping process to cut a small amount of material along the outline or inner outline, so as to reduce the surface roughness and improve the verticality. In general, the renovation process also improves the dimensional accuracy at the same time.
34 turning hole
It is a stamping process to turn the material into a short side or flange along the shape curve or around the inner hole.
35 deep drawing
It is a stamping process to change the straight wool or working parts into hollow parts, or to further change the shape and size of hollow parts. Space-time core in deep drawing mainly depends on the bottom of punch.

What are the processing principles of machining

First, in order to ensure the processing accuracy, rough and finish processing should be carried out separately. Because of the large amount of cutting, the large cutting force, clamping force, heat generation, and the remarkable hardening phenomenon on the machined surface, there are large internal stresses in the workpiece. If rough and rough machining are carried out continuously, the precision of the finished parts will be lost quickly because of the redistribution of stress. For some parts requiring high processing accuracy. After roughing and before finishing, low temperature annealing or aging should be arranged to eliminate internal stress.CNC Machining

2. Reasonable selection of equipment. Rough processing in machine parts processing plants mainly cuts off most of the processing allowance, and does not require higher processing accuracy. Therefore, rough processing should be carried out on machine tools with high power and low accuracy, while finishing processes require higher accuracy. Rough and finish machining are processed on different machine tools, which can not only give full play to equipment capacity, but also prolong the service life of precision machine tools.

Carbon steel turning and milling machine processing

3. Heat treatment process is often arranged in the process route of mechanical processing. The position of heat treatment process is arranged as follows: in order to improve the cutting performance of metals, such as annealing, normalizing, tempering, etc., it is generally arranged before mechanical processing. In order to eliminate internal stress, such as aging treatment, quenching and tempering treatment, it is generally arranged after rough processing and before finishing. In order to improve the mechanical properties of parts, such as carburizing, quenching, tempering, etc., it is generally arranged after mechanical processing. If there is large deformation after heat treatment, the final processing procedure should also be arranged.

Properties and Advantages of Titanium Basket

Titanium Basket Performance, Advantages and Use Notes I. Introduction of Titanium Basket

Titanium basket is composed of titanium plate and titanium mesh. The thickness of titanium is between 0.5 mm and 2 mm. Abstracts from: (http://www.chinatzsb.cn) China Painting Equipment Network. The common meshes of titanium baskets are 6mm *3mm, 10mm *3mm, 10mm *5mm, and the wider sixteen mm *8mm, 25mm *15mm, etc.

Titanium baskets have high strength, light weight, corrosion resistance and oxide film on the surface. Under normal plating conditions, this film can prevent current from passing through the titanium baskets and direct current to the anode material in the titanium baskets.

There are various types of titanium baskets, including round, rectangular, dish, etc. Special design can also be made according to the requirements of the product.

Titanium baskets are usually used in conjunction with anode bags. Anode bags are usually made of polyester (polyester) or polypropylene (polypropylene) fibers with acid and alkali corrosion resistance or oxidation resistance, which are coated outside the titanium basket to prevent impurities such as anode sludge from mixing into the tank. Sometimes, in order to prevent the slime from burring, double-layer anode bag can be used. When using double-layer bags, the inner bags should be tightened and the outer bags should be looser. Anode bags should have good corrosion resistance, wear resistance and elasticity.

2. Advantages of using titanium baskets

1. Effective control of the ratio of anode to anode area

2. Anodic dissolution is good and less anodic slime is produced.

3. It is convenient to load or supplement anode materials. Anode maintenance is also relatively simple

4. Anode material can be used adequately and corner material can be used to save energy consumption and reduce cost.

5. It can prevent the uneven current distribution caused by the dissolution of the lower part when using the anode plate or strip.

6. Improving the load capacity of the anode, increasing the area of the soluble anode and reducing the passivation of the anode

7. Continuous deposition, balanced flow distribution, high anode efficiency, low voltage loss and low consumption

3. Key Points of Titanium Basket Design

1. The conductivity of titanium is poor. Generally, the electric current of the hook outside the water is not more than 0.24A/mm2, and the electric current of the hook in the water is not more than 1.5A/mm2. Otherwise, the heating of the hook will cause the temperature of the electroplating solution to rise, the refrigeration capacity to increase, the waste of electricity and even the plastic tank to be damaged by heating.

2. Titanium basket hooks and electrodes do not generally use plane or circular contact, which is liable to cause poor contact and lead to spot corrosion of the electrodes.

IV. Notices for Use of Titanium Baskets

1. Titanium baskets and anode bags are immersed in 10% alkali solution for 6-8 hours, washed and dried, and then immersed in 5% dilute sulfuric acid.

2. When the titanium basket hook is obviously heated, it can increase the number of titanium basket or increase the cross-section size of titanium basket hook to improve the conductivity of titanium basket.

3. Titanium baskets should be slightly higher than the liquid level of 30-40 mm in order to prevent the outflow of anode slag.

4. The lower end of the titanium basket should be higher than 100-150 mm of the parts (shade can be added near the liquid level), so as to avoid excessive concentration of the current of the parts at the lower end and cause burning.

5. Titanium baskets should be in close contact with the anode. Otherwise, the anode potential on the titanium baskets will rise sharply, resulting in oxygen evolution and chlorine evolution reaction on the surface of the titanium baskets, resulting in damage to the titanium baskets and oxidation of additives.

6. Titanium baskets should be wrapped tightly in anode bags. A few centimeters gap should be left at the bottom of the bags to store the anode sludge that may be produced.

7. Clean the anode bags and titanium baskets every half month to one month, and replace the damaged anode bags to ensure that the bath and bath are free from pollution.

8. Replenish or enrich anode materials in time so as to avoid overhead when nickel is insufficient, otherwise titanium will be eroded.

Introduction of Zirconium Baskets

Zirconium can withstand the corrosion of fluoroboric acid (HBF4). The corrosion resistance of sulfuric acid (H2SO4), boric acid (H3BO3), hydrochloric acid (HCI), sulfonic acid and their salts is more than 10 times that of titanium metal. It is an ideal tool for the tin plating process of circuit boards. Compared with the process of directly using tin bars as anode tin plating, its stable anode area not only ensures the uniformity of tin film, but also saves the loss of plating solution.

Technical Level of Hardware Stamping

Because many stamping factories belong to the main engine factories, the stamping parts market is very imperfect and sound. But the market of small stamping parts is very mature in some areas in the south. From the current situation, there are the following problems in stamping parts market in China:

(1) Some production capacity is in excess of demand, and some stamping factories in the main engine factories are unable to let go and hold them. For most of the year, production tasks are insufficient and there is no market behavior.

(2) The market competition in the stamping parts industry of household appliances and electrical appliances is fierce. However, there are not many enterprises with international competitiveness in Chengdu. (3) Seriously studying the stamping parts market has not been carried out. Stamping parts market is chaotic. In the above market conditions, technological development is limited and the whole industry lags behind, as shown in:

(1) The overall level is low, many industries have excessive production capacity and lack of high-grade technology. Technological progress is slow.

(2) Material technology, die technology, lubrication technology and equipment are at a low level, far from meeting the needs of domestic production and development.

Introduction of elbow

brief introduction

Elbow is a kind of pipe fittings commonly used in plumbing installation. It is used to connect the bends of pipes and change the direction of pipes.

Other names: 90 degree elbow, right angle elbow, love and bend, stamping elbow, pressing elbow, mechanism elbow, welding elbow, etc.

Usage: Connect two pipes with the same or different nominal diameter to make the pipes turn at 90, 45, 180 degrees and various degrees.

The bending radius less than 1.5 times of the pipe diameter belongs to elbow, and the bending radius greater than 1.5 times of the pipe diameter belongs to elbow.

purpose

A kind of pipe fittings commonly used in pipeline installation is to connect two pipes with the same or different nominal diameter so as to make the pipeline turn at a certain angle and the nominal pressure is 1-1.6 Mpa.

Skills of manual tapping of fasteners and solutions to common problems

Tapping is a metal cutting process in which the tap is rotated into the bottom hole of the embryo of the fastener to be drilled by a certain torque to produce the internal thread. In traditional fastener manufacturing, manual tapping machine is often used for thread processing. Because in actual production, some threaded holes are not suitable for milling threads because of their location or part shape limitations. Tapping machine is a kind of machine tool which processes internal threads with taps, but sometimes in the process of tapping, the breakage of taps caused by various factors causes a lot of waste. Following is a brief introduction to the traditional manual tapping techniques and precautions of Borun Petrochemical Company.

I. Steps and Skills of Manual Tapping

The quality of manual tapping is greatly influenced by human factors, and the strength of taps with small diameter of threaded holes is low. Therefore, only by adopting correct methods can we ensure the quality of the workpiece manually tapped by fasteners.

(1) clamping of workpiece

Workpiece clamping should generally place the threaded side of the workpiece in a horizontal or vertical position. It is easy to judge and keep the tap perpendicular to the base surface of the workpiece.

(2) Location of taps

At the beginning of tapping the thread, the tap should be set straight, and then one hand to hold the tap and the other hand to turn the hinge gently. Observing whether the tap is perpendicular to the base surface of the workpiece from the front or side, and correcting it with a right-angle ruler when necessary, the direction of the tap is basically determined.

(3) Revision of taps

If the tap position is incorrect at the beginning of tapping, the tap can be screwed out with two cones to correct and then tapped with the head cone. When the cutting part of the tap enters the workpiece, it is no longer necessary to apply axial force to automatically screw in by the thread.

(4) Taper stability

When turning the hinges evenly, the operator’s hands should be balanced. Do not use too much force and sway left and right. Otherwise, it is easy to tear the threaded teeth and lead to the expansion of threaded holes and taper, and the tap will be broken.

(5) Withdrawal of tap

The screw tap is loosened with the hinged screw, and then the screw tap is screwed out, because the combination of the tapped threaded hole and the screw tap is looser. Avoid swing and vibration of tap when withdrawing, thus destroying the surface roughness of thread.

2. Treatment of tap breakage

The reasons affecting the quality of machine tool taps include: main materials, CNC tool design, heat treatment, processing accuracy, coating quality and so on. For example, the size difference of the taper section transition is too big or the transition fillet is not designed, which leads to stress concentration. When used, it is easy to fracture at the stress concentration.

(1) Technological factors of taps

Cracks in taps may occur if the taps are not preheated, quenched or overheated, tempered in time and cleaned prematurely before quenching.

(2) Selection factors of taps

For tapping parts with too high hardness, high-quality machine tool taps should be selected, such as cobalt-containing high-speed steel wire taps, carbide taps, coated taps, etc. The number, size and angle of chip removal slots of taps have an impact on chip removal performance.

(3) Material factors of workpiece

With the emergence of new workpiece raw materials, the variety of tool materials is also increasing, which requires the selection of appropriate taps before tapping. When the tapping material is impure, there are some hard spots or air holes in the part, which will cause the tap to lose its balance and break instantly.

(4) Performance factors of machine tools

Machine tools and grippers are also very important, especially for high-quality taps, as long as the accuracy of the machine tools and grippers can play the performance of taps. When tapping, that is, the axis of spindle is not concentric with the center line of bottom hole. Torque is too large during tapping, which is the main reason for tap breakage.

Selection of Special Tapping Oil

Tapping oil is the lubricating medium that must be used in thread cutting process of fasteners. High precision thread cutting process has higher requirements on cooling, lubrication, penetration and cleaning performance of tapping oil. When using waste engine oil and vegetable oil instead of special tapping oil, it is easy to have bad conditions such as burrs, and the tap life will be greatly reduced.

(1) High efficiency tapping oil has super lubricity, low friction coefficient and high extreme pressure.

(2) The special tapping oil film has strong adhesion and toughness, which can effectively protect the tap and improve the thread quality.

(3) Good cold removal performance can effectively inhibit the rise of temperature, reduce sintering and jamming, and has special effect in reducing cutting edge and broken tap.

(4) The use of special tapping oil to remove chips is more smoothly. During tapping process, a large number of iron chips will be produced. The iron chips are easy to stick to the thread hole and the top of the tap. At this time, the iron chips must be washed away with special tapping oil.

(5) Due to the use of non-corrosive vulcanization additives as the main agent, the special tapping oil has no odor and does not irritate the skin, which can effectively avoid workers’skin allergies and other problems.

What are the types of stamping parts for hardware and crafts

Stamping is the production technology of product parts with certain shape, size and performance by means of the power of conventional or special stamping equipment, so that the sheet metal is directly subjected to deformation force and deformation in the die.

Stamping is a method of metal cold deformation processing, referred to as stamping. It is one of the main methods of metal plastic processing (or pressure processing).

“Hardware stamping products – tokens and medals”

“Hardware handicraft” stamping parts refer to the tools or handicraft made by processing and casting gold, silver, copper, iron, tin and other metals to fix things, process things, decoration and so on. What kinds of stamping parts of Hardware handicraft are there?

1. Tin parts – tin is not widely used. The common tin parts are canned bottle caps, tin paper, plastic bottle tin seals, etc.

2. Gold articles – As we all know, gold is a valuable precious metal with a value of 385 yuan per gram. Most of them are deposited in the national treasury for good preservation. Most of them are gold. Gold is naturally used to make valuable goods. Gold casting objects are usually jewelry, money, substitute money and other items, such as rings, necklaces, gold coins (ancient times), bricks, bars, etc. There are also some objects used to make celestial spheres and other objects.

3. Iron castings-iron has a very wide range of applications, and its content in the world is very large: the proven reserves of iron ore in the world have exceeded 200 billion tons! There are two kinds of iron commonly used: hematite and magnetite.

Hematite: The composition of hematite is iron oxide, which is dark red or steel gray. It uses cast iron nails, screws, nuts, hammer heads, machine parts and so on.

Magnetite: Magnetite is magnetic, also known as “magnetite”, “magnetite”. Magnetite is not as widely used as hematite, but also useful. Magnetite can be stereotyped into magnetite identification object.

4. Silver-silver is silver-white, and it is also a precious metal. In ancient China, it was used to make silver treasures or broken silver for national expenditure and daily trading. Ancient Egyptians used silver as silver tablets to treat wounds by using its water-soluble silver ion bactericidal effect. Modern silver is also commonly used in jewelry processing. Silver has excellent conductivity and heat transfer performance. Common industrial silver parts are usually parts of electronic instruments and power generation equipment, such as silver core wires.

5. Copper is the messenger of human civilization. Ancient people often used copper to make ritual utensils, such as copper tripod and modern tools. As we all know, copper has excellent electrical conductivity, second only to silver, but copper ore is more and cheaper than silver ore. Copper is often used to make wire cores and parts of communication equipment and electronic equipment.

Normal operation of twin screw extruder and matters needing attention

Normal operation of twin screw extruder

When the twin screw extruder is in normal operation, the following items should be paid attention to frequently:

(1) Through the window of the upper part of the feeding port, observe whether the feeding condition of the material is stable and even declining.

(2) Monitor the operation of the screw-driven motor, whether the current value has abnormal changes.

(3) Monitor the temperature and head pressure display in each heating area and record the working status of the instrument regularly, record the actual indicative value, pay attention to the alarm signal exceeding the limit, and deal with the abnormal situation in time.

(4) Monitor the temperature, abnormal noise and vibration of motor, reducer bearing and other parts.

(5) Pay attention to the leakage of melt in the head and other joints.

(6) Pay attention to the working condition of the cooling system and whether it plays the role of regulating the temperature.

Monthly Archive July 27, 2019

Analysis of the Common Defects in Zinc Alloy Die Castings

Application of Cast Iron Drainage Pipe

Common technical terms for metal stamping dies

What are the processing principles of machining

Properties and Advantages of Titanium Basket

Technical Level of Hardware Stamping

Introduction of elbow

Skills of manual tapping of fasteners and solutions to common problems

What are the types of stamping parts for hardware and crafts

Normal operation of twin screw extruder and matters needing attention

CNC Machining parts

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