Machining is an operation that changes the shape, surface finish, and/or mechanical properties of a material by the application of special tools and equipment.
This is typically carried out by machines where a cutting tool removes material to effect the required change to the work piece. Tens (hundreds?) of factories in China do this type of operation.
Different shapes can be formed by different processes; some typical processes that you will find in many Chinese factories are highlighted below:
- Laser Engraving
- EDM (Electronic Discharge Machine)
In this type of audit, we focus on metal machining.
Low-tech machinery vs. computer numerical control (CNC) machines
The majority of the processes listed above can be achieved through CNC machines with multiple axis functionality (e.g. the 5-axis machining centre). This has become quite standard, in China like in the West.
With CNC machines, component manufacture is highly automated using computer-aided design (CAD) and computer-aided manufacturing (CAM) programs.
The machines come in different sizes and functionality. The 3 axis CNC milling, for example is similar, to conventional milling in that all movements are in 3 axis only (X, Y, Z, left-right, forward-backwards, up-down).
A typical 3-axis CNC machine will cost from 25,000 USD upwards, depending upon make and specification.
The 5 axis CNC machining centre is a CNC milling machine that is capable of using the conventional 3 axis – x, y and z (left-right, forward-backwards, up-down), but has an additional 2 axis of movement in the ability for both the table and the head to swivel. This allows the head and table to be moved around as the other axis are being fed allowing undercuts to be machined and allowing machining on multiple faces of the work piece.
A typical 5-axis CNC machine will cost from 75,000 USD upwards, depending upon make and specification.
Advantages of using CNC machines
Manufacturers usually decide to invest based on three advantages:
- CNC machines can be run 24 hours a day, 7 days a week, and 365 days a year. One human operator can supervise several CNC machines.
- Once the computer program has been compiled and the product verified against specification, a CNC machine will manufacture the same part continuously to the same specification. This equates decreased rejects which leads to reduced costs for the manufacturer.
- CNC machining is generally carried out at high speed (12,000 rpm), so the part cycle time is reduced, again leading to greater output and lower costs per piece.
However, having all this latest technology does not guarantee ‘quality’ products at the end of the day.
How to audit metal machining processes
As I wrote above, it takes more than the latest CNC machines to make products that meet your specifications reliably and consistently. It is the holistic procedures and processes within an organization that provides the ‘quality’ product you are looking for.
Our engineers report back on detailed checklists that are organized in 9 sections:
- Material Controls
- Drawing Instructions
- Capacity & Planning
- Post Machining
- Process Control
- Quality Inspection
The idea is to have more than just the information a new supplier is willing to disclose in its marketing materials. It is also helpful to show your current manufacturers where they can improve.