precision machining

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Incoming processing and machining production

When we make small parts, the fixture is relatively simple, and too complex fixtures will bring more uncertainty to the machining. In mass production (such as mobile phone buttons and other parts that need to be delivered tens of thousands of goods a day

The selection of positioning and clamping solutions for small parts machining by manufacturers of incoming and in-feed machining  

 When we make small parts, the fixture is relatively simple, and too complex fixtures will bring more uncertainty to the machining. In mass production (such as mobile phone buttons and other parts that need to be delivered tens of thousands of goods a day), it is first necessary to consider ensuring the stability of the fixture.

For small parts fixtures, the parts themselves are relatively small in size, and it is difficult to design the positioning and clamping mechanism, and hydraulic systems are not used. At the same time, the production cycle is relatively short, usually about three months to update the fixture, generally we will use mechanical locking mechanism, screws, pressure plates, springs, etc. Use air cylinders to fix the entire fixture board on the workbench, the base, and the pneumatic occasion is relatively small.

Larger mobile phone parts such as mobile phone cases need to be compressed by a pneumatic mechanism.   

For example, the mobile phone camera is a part of about 10mm, and the fixed position is limited, and all such parts will be processed. Other parts may stamp blanks made of powder metallurgy.

The precision of the blanks is not accurate and the fixing position of the fixture is very limited. If the cylinder is used, the efficiency is high, but the clamping force of the cylinder is too small, and the number of processed parts is small if it is too large. One part and 20 parts are made on the machine, and the efficiency of tool change time will be much worse.

The advantage of the more parts we make is that the machining time will be less, including some other time for tool change. Although the drilling and tapping machine uses a lot of tools, it is possible to use more than a dozen, then we can only reduce this waste of tool change time by installing more parts on the workbench. If we make buttons, we can make hundreds of parts at once. For example, it usually takes less than one minute to process the volume button and power button on a mobile phone, so the efficiency is very high.  About the design of small parts fixture  For our mobile phone small parts industry, it may need to be updated as soon as three months. Now many of the industry uses some relatively low-cost materials for manufacturing.

For example, the base of the mobile phone case is basically fixed, and then the positioning plate is changed to the corresponding one after changing a part, and then the cylinder is adjusted to reduce the production cycle and cost of the fixture.   If it is a general-purpose part, we will adopt the design of the first set of fixtures, and then the subsequent processes will be arranged according to this set of fixtures.

Anyway, the machining technology is basically the same, and the universal fixture is as common as possible. Because the competition in this industry is fierce, the delivery time required by customers is very short. It is possible to give the drawing today and ask for the product in three days.


Moreover, our own factory does not have the ability to make large batches of fixtures. There are only machining centers and lathes here. If we make fixtures now, we will use grinders and other machine tools.   

Wire cutting and heat treatment are not available to us. If it is to be shipped out, there will be a very long cycle. A set of fixtures may have a lot of parts, like we did before, a set of fixtures may have one or two hundred parts. The manufacturing cycle of parts may be relatively long, and the supplier may not be able to supply the goods.

Because you think about it, if you put in two hundred sets of fixtures, from the material to the completion of the assembly, there will be heat treatment, finishing and many other processes in the middle.  

Choose the clamping force of small parts  

The clamping force of small parts mainly has several aspects. First, we will add a process to him, for example, a button is a set, but we will arrange this part on a whole board, and then through the positioning hole, use a vacuum to suck it for cutting. In this way, the whole plate machining and fixing will be very effective, and there will be no failure to clamp. From the very beginning, it is a board, to the last process, we will use stamping or precision carving to cut into one by one before assembling.

This can save clamping time and ensure the effective clamping and fixing of the fixture. Regarding the fixture design of (stainless steel) multi-structure parts, like mobile phones, some other structural parts may be stainless steel. If there are many structures, the customer will develop powder metallurgy, and use the metal stainless steel with other binders and some auxiliary things for injection molding. ,

Then vacuum sintering, and finally shaping, just like plastic plastic, but during the sintering process, the binder will volatilize, and finally the metal will remain.   

This kind of parts will be slightly more complicated in positioning and fixture design. Because the positioning and size of the blanks sintered by itself are not very accurate, at least not all processed materials are so accurate. When designing this type of fixture, we may have requirements for the blank, and the accuracy of positioning is difficult to grasp.

Especially what we are doing is exterior parts. For example, mobile phone cameras need to make a round of highlight chamfering. This chamfer is not like the deburring corner of ordinary parts, and the appearance requirements will be higher.

The chamfer around the iPhone5's fuselage, if it is offset by 5 wires from the left and right, will produce a more obvious unsightly visual effect. If it is a few wires on other parts, it may have little effect, but for appearance parts, if the general customer requires it to be controlled within a millimeter tolerance, the requirements for ingredients will be very, very high. For some things that we really can't do, we will use some more complicated methods, such as online measurement. .

Figure 1 iPhone highlight chamfer   

The determination of the process  

For the fixture, the process is actually more important. Usually in the mass production process, we will prioritize the machining technology, and then design the fixture according to the machining sequence. Because if the workmanship is not good, it will cause a lot of waste, such as the efficiency is not reached, the tool and machine tool wear is relatively large. If you make a mobile phone case, if you do not need to measure the highlights, the scrap rate may be even higher. Because the cost of the last two high-gloss processes of a mobile phone case has reached almost 100 yuan, if it is scrapped at the last step, the first dozen processes are wasted.

Regarding the batch machining of small parts     

For parts, we usually make small parts larger and break them into whole pieces, so that the small parts are concentrated in the same process connection material. Otherwise, the use of a single machining efficiency will be very low, the design of the fixture will become complicated, and at the same time, the operator of the clamping will be more difficult and easy to fatigue. Usually we use process connection materials, such as some buttons on mobile phones, camera rings, and card holders. Basically, the parts are connected and the whole board is made. In this way, the machining efficiency and dimensional stability will be much better. But the incoming material is a relatively complicated part with a single design.

It needs to be processed by some special mechanisms, such as clamping this piece, usually using some spring mechanism, then adding a tilt transmission mechanism, and adding an auxiliary clamping structure to complete it together.   Regarding the process and tool control in the machining process    

The size of the blank must be controlled. First, the fixture positioning must be accurate, which is a basis. Then there is the control of the positioning size. For example, the positioning hole needs a reamer to ensure the aperture, and the important size of the tool needs to be added with a fine knife, and two to three are used to process. Tool life control is set on the machine tool.

For example, a technician needs to change the tool when it reaches one thousand. In many cases, dimensional stability must be fully verified. For example, we need to perform cpk size analysis to verify the stability of our manufacturing process, including tools and fixtures, which must be verified. What an impact.

Some parts will be deformed after machining the size of the previous process may be good, and the subsequent process will cause deformation. For the coefficient, it will take many verifications to find out. Adjust the front size and finish machining later to ensure that it is within the tolerance range.

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