Improving machinability through tolerance management

Design engineers do not always have the necessary experience of materials, processes and treatments to design products that require minimal engineering changes, keeping scrap and wastage to a minimum. One of the ways this problem can be overcome is to provide the designer with the expertise of a manufacturing or machining professional. By means of good communications and the correct application of tolerancing, it is possible to predict and, therefore, improve machinability.

1 - Provide feedback

The first point is to provide the designer with feedback from the machine shop and associated manufacturing specialists. They are unlikely to take offence when someone suggests a change, as an improved design can only reflect well on both the design and manufacturing functions.

2 - Invite the designer to spend time on the shop floor

It is a good idea to invite the designer to spend a few days helping a machinist make one of the more complex parts. As part of this process, encourage the designer to tell the machinist which features are absolutely necessary and which can be tweaked: he or she may well have some good suggestions to improve the machinability. The machinist may be able to tell the designer that a particular aspect of a component is challenging, resulting in a simplified design.

3 - Invest in the right tolerancing software

Parts that do not fit together are not necessarily the fault of the manufacturing department. Get the designer to double-check the tolerance stack, and then check it again, visualise it and write it down. Encourage the designer to invest in good tolerancing software and offer to part-fund it from the manufacturing budget.

Bear in mind that, in tolerancing stack design, it is absolutely crucial that any software employs capable tolerances. If it does not, it really is not worth the code it is written in. If it does not work with capable tolerances, then it needs to be used alongside Tolcap, which will allocate process-capable tolerances to any design characteristic. Tolcap manages tolerance allocation and predicts process capability at the early stages of design before production starts. This reduces production costs, improves product quality and increases product profit. The software is web-based, readily usable and fully supported for business and also for the education and training of engineering students. [Follow the link to find out about the Free trial of Tolcap - Ed]

4 - Consider material and process

The designer should consider the material and process as a priority. If the material is not crucial to the design, encourage the designer to choose the easiest material to machine. This will reduce capital expenditure as well as reducing scrap and wastage attributable to machining difficulties.

Equally, if the process is producing a tolerance that is better than required, choose a different process to reduce the cost. It may well be that the component does not really require a fine process, such as grinding, for instance. Good tolerancing software will help you select the right process and material; by predicting tolerance you can choose exactly the right level of accuracy, without expensive over-specification.

5 - Spend time with the quality assurance department

While your new part is being qualified and tested, encourage the designer to spend time with the quality assurance team and whoever handles industrial compliance in the business. It is not worth producing an easily machinable part if it does not have the physical attribute required to pass muster and reach the end user.

Of course, if you work in a multinational manufacturing organisation, many of these suggestions are nothing short of Utopian. The design department may be on a different site from the production plant - or even in a different country! So having the designer spend time with the machinist is always impossible.

If this is the case, then point three is the only way in which you can get the benefits that closer integration would bring. By investing in tolerancing software, such as Tolcap, far fewer potential problems will get through to the shop floor. As a result, the potential waste is never produced and the product is more elegant, more efficient and less costly. No matter whether the product is very sophisticated or a simple component, and irrespective of whether you are using Tolcap in Rolls Royce or Dyson or on behalf of a micro manufacturer, the enormous costs of engineering change, rework and scrap will be reduced.

Follow the first link to find out more about Tolcap tolerance management or follow the second link to find out about the Free trial of Tolcap.