For a layman who is not familiar with CNC machine shop operations, once the chips stop flying apart, the CNC milled part drops, and another precision machine tool part is introduced, they may think that the final product is accurate and meets the specifications. Unfortunately, this is not always the case. In any relevant CNC machine shop, the finished product will not be delivered to the customer until it has passed the inspection service process. The dimensions of the part must conform to the tolerances set by its design, including a thorough check of the finish of all machined surfaces.
In general, parts may conform to a specific size, but must be scrapped due to substandard overall appearance and surface finish. Not only does this lead to aesthetic problems, but more importantly, it negatively affects the functionality of the part.
On top of that, at the final stage of the milling and machining process, the amount of work that has to be sent to the bin is less than expected. CNC machinists are naturally detail-oriented, take pride in their work, and want to see a complete project. Scrap parts due to surface finish issues can also be a real profit killer for job shops. Poor quality can lead to increased costs, increased downtime, delayed deliveries, and in the worst case, lost orders.
Increase tool speed
Faster speeds (in surface feet per minute) mean less contact time between the material and the cutting tool. This reduces edge build-up that leads to poor surface finish and extends the life of the tool. Tool failure is a major cause of damage to precision machined parts. Never estimate or guess the speed required for your work.
Always clear/control the chip
Removing excess chips or accumulated edges during machining and not allowing them to touch the workpiece is a critical task and the key to producing a high-quality surface finish. Chips and BUEs tend to build up and can easily damage the surface finish of the tool if not removed. Chip breakers, compressed air and best of all, overflowing coolant can be used to remove chips for better control and to reduce scratching/damage to parts.
Different tools should be used for roughing and finishing
Don't use the same tools as roughing to complete CNC precision machining services. Instead, a small number of roughing tools should be used to remove most of the material, while newer, sharper tools should be kept and used only for finishing. When used in conjunction with roughing or finishing tools, the tool insert radius, rake angle, feed rate, and insert material itself can result in higher quality.
For the uninitiated, once the milling process is complete and the delivery date is approaching, it seems that only the aesthetics of the precision machined parts need to be checked. Regardless of the material, a thorough inspection of the finished work is a key factor in influencing the functionality of a part. It is particularly suitable for the aerospace and medical device manufacturing industries. Too many chips, slower running speeds, and improper tool use are the main causes of deterioration in surface finish. Lack of machine maintenance, low coolant levels, improper setup, and CNC programming errors are also contributing to this.