How WayKen Controls Quality Across High-Mix, Low-Volume Robot Parts Production

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Manufacturing of robot parts on a high mix low volume basis poses a problem for maintaining quality, because different parts may require different materials, machining operations, tolerances, and surface finishes. In contrast to mass manufacturing where processes have already been established, manufacturing of each new part may pose a new manufacturing risk. It is therefore important to control the process before, during, and after machining to achieve high precision machined parts.

Process Scheduling – Develop an Efficient Machining Plan

A high-mix production order might have different drawings, materials, number of pieces, and finishing requirements. Considering all of them separately without a proper process plan raises risks of improper tool selection, incorrect following of the drawing specifications, inappropriate set-up, and non-optimized production time.

A precision metal parts machining process should define the sequence of operations, clamping approach, machining datums, tool selection, inspection points, and finishing requirements before the process starts. Sometimes, parts with common material or similar processing requirements can be grouped together to reduce the number of setup changes, whereas some complicated products may need individual fixturing and machining approaches.

Material properties also have an impact on scheduling. Brass CNC machining, for instance, is usually efficient due to good machinability of this material, although small size brass parts might experience burr formation, deformation, and problems related to chip production near threads and other small features. WayKen managed a 2,000-piece brass connector project with custom fixtures and two stages machining schedule by choosing 25 parts to be scheduled per setup.

Surface Finish and Dimensional Accuracy Control

How WayKen Controls Quality Across High-Mix, Low-Volume Robot Parts Production

The surface finish is not only an aesthetic issue. Depending on the application, the surface might have a role of the sealing face, bearing area, assembly surface, or external visual surface, hence the required level of roughness will vary within one part. This means that machining settings, tools, the way of finishing and other post-machining operations should match the purpose of each surface.

Dimensional control also becomes more challenging when parts are subjected to several operations. It may happen that the feature is machined properly, but due to anodizing, coating, heat treatment or some other kind of finishing process, it will become inaccurate afterwards. It should be taken into account before the finishing operation rather than found during the final inspection.

One of WayKen’s robotic projects featured the parts which required different finishing operations depending on whether they were meant to be visualized, mated or sealed. In a modular robot project, the drawings showed the places where sand blasting was not allowed so that the machining roughness was retained. And these were documented across production stages so operators and QC personnel could verify each treatment.

For precision metal parts machining, the control of the correlation between dimensional requirements and surface treatment becomes crucial since the finished part must satisfy both requirements.

Quality Control Throughout the Entire Production Process

The quality control procedure can be enhanced through distribution of inspections throughout the manufacturing cycle instead of focusing them at the end of production. Inspection of the incoming material ensures that the desired quality level is achieved, the first-article inspection confirms the machining process and the in-process inspection detects deviations from the desired dimensions before affecting the whole batch.

This is very important in low-volume production where a single faulty part may constitute a considerable proportion of the number available. Hence inspection plans must define critical dimensions, inspection method, frequency and acceptance criteria before initiating production.

Wayken employs a production quality control plan for incoming material, process control, appearance and shipment. In one low-volume medical robot where there were 18 part types manufactured, the first article inspection was done before continuing with production.

Whenever a deviation from the tolerance range was detected during inspection, machining parameters were adjusted before continuing with production of the rest of the parts. This is true for high precision machined parts too where inspection data feeds back into the process, and not just record whether a finished component passed or failed.

Conclusion

High mix-low volume production of robots entails a manufacturing control system which must be flexible to cope with variations in the nature of the components without fragmenting the quality criteria. Efficient scheduling ensures proper process control, while surface and dimensional control ensure functional specifications are achieved, and inspection at various stages prevents any spread of faults. This is true for brass CNC machining and other specialized operations.