How do I Select a Machining Supplier?
This article reviews the criteria affecting the selection of a machining supplier.
We hope that this information can be helpful to you, even if you are already familiar with some of it. 
In machining, there are no shelf products that can be selected out of a catalog, but rather “orders based on shop drawings”. Therefore, the product cannot be inspected before being purchased, which can sometimes lead to uncertainty about the final result that will be obtained.
Every vendor is different. Therefore, as a customer, your purchase personnel should be very familiar with the type of manufacturing required for your parts and contact the most suitable vendor accordingly.
The first criterion – the manufacturer’s size
Normally, the work performed by machining consumers can be divided into the following categories:
1. Companies involved in development only. 
2. Companies involved in serial manufacturing (with or without the development stage). 
The purchase personnel of a company involved in development only would prefer contacting a machining vendor who is a workshop. In this way the company will benefit from the shortest possible delivery time and relatively low prices.
In contrast, the purchase personnel of a company involved in mass production would contact a medium or large manufacturing plant with mass production capabilities.
If a small machining workshop takes upon itself to perform a large job, it actually blocks itself from providing its services to other customers.

The second criterion – standards

Certain fields (aviation, medicine, etc.) require standards such as ISO as a necessity. Some companies require their vendors to uphold certain standards, clearly making them into mandatory criteria.
Achieving and maintaining such standards clearly indicates the relatively high quality of the vendor’s products. However, they also cost a considerable amount of money, and this must be taken into account. Therefore, when contacting a machining vendor with high standards, it is recommended to take into account that if they are not mandatory, you me be paying for something that is unnecessary.

The third criterion – types of raw materials
Raw materials can be divided into three categories: aluminum, steel and plastic.
Most machining plants are constructed for the use of aluminum as raw material and prefer doing so. This is because its processing is easy due to its softness, and does not require frequent replacement of processing tools as a result of increased wear and erosion. Additionally, with aluminum the manufacturer can streamline its technology and significantly reduce the time consumed by each machine.
Aluminum processing machines work at high speeds of at least 8,000 rpm. In comparison, steel processing machines (and machines for other hard metals) run at no more than 6,000 rpm and have a high torque property (the power applied to removing a chip). To illustrate, it is relatively easy to cause the motion of the processing tool to stop in an aluminum processing machine, if you overstrain it.
Therefore, if the products you need to produce are based purely on steel and other hard metals, you should select a machining vendor who can work with these raw materials.
As to the category of plastic raw materials (peek, Teflon, PVC, epoxy glass, etc.), the manufacturer should be experienced in processing them, as some of these materials change their dimensions after processing is complete, which must be taken into account in advance.
In addition, certain materials in this category lead to the accumulation of minute dust particles, requiring a special drawing device that prevents them from penetrating the machine so as to ensure distorted products and possible damage to equipment do not occur.

The fourth criterion – machine size

Some fields, particularly medical ones, require very small machining items to be produced (such as dental implants). On the other hand, other fields require parts that are larger than 1,000 mm.
Due to the necessity of the CNC machine to move over very short distances many times (where miniature pieces are concerned), a special machine called the Swiss Type has been developed. Larger parts (over 5 mm) can easily be produced using “normal” machines, where parts up to about 1,000 mm long are normally produced by milling, and up to 300 mm long by turning. Beyond these dimensions, the machines required are not owned by most manufacturing plants.

The fifth criterion – the parts’ complexity

CNC machines can move over several plains. A basic machine moves over three plains (on three axes).
Some parts require “sculpturing” (creating rounded surfaces where the arch is not uniform and has a variable radius). In such a case, a capability to move on additional axes is required. Currently, machines with the capability to move on five axes are classified as advanced machines that can produce anything. Of course, the programmer’s ability is crucial, and some programmers can produce parts that are highly complex on machines that are considered to be quite simple.
However, in most cases more than three axes are required in order to achieve the desired result. One of the reasons is that machines with five axes permit their user to process the part without having to release it from the machine in order to mount it in a different angle, an action that can lead to impaired dimensions.
Some manufacturers have lathes that also mill (“milling lathe”). These machines are very useful, for example for rounded (cylindrical) parts with two or more different centers. With a milling lathe, such parts can be produced with great success.
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​The sixth criterion – equipment for testing and quality control
As production is achieved by computerized machines that are extremely precise (up to hundredths and thousandths of mm), the best way to test parts is by a computerized machine called an XYZ.
This is in fact a “robot” performing the test by touching many different points after the part’s dimensions are provided.
This equipment is particularly expensive and requires maintenance, calibration and skilled workers – therefore not every manufacturer has it. But with parts that are very accurate and complex, there is no other choice but to test them this way. Therefore, it is important to ensure the manufacturer you intend to use has this machine.
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