Tooling challenges met

Thetford-based Instrument Machining Service specialises in the manufacture of components for the aerospace, motorsport and precision components sectors, mainly for the after-market and repair markets, using a variety of conventional and CNC machine tools. Many of the parts manufactured are small in size, such as nuts, bolts, washers, spring guides and bushes. Due to the applications they are used in, they have to be manufactured to the same strict aerospace specifications and tight tolerancing as what might be considered more glamorous parts. Image: By employing modern tooling technology on its existing machines, Instrument Machining Service was better placed to make investment decisions when considering new equipment Over the past few years, and under the guidance of managing director Glen Parfett and assistant manager Dean Smith, the 15-employee business has undertaken a radical review of its manufacturing processes. The result is a dramatic improvement in productivity and workflow. The company has looked at all aspects of its business, which has seen a greater involvement of all of the staff, a programme of training that has ensured a greater degree of multi-skilling on the shopfloor and investment in machine tools. However, one of the biggest catalysts for change has been a review of its cutting tool application. DEMAND PROMPTS ACTION As part of this review, Instrument Machining Service has made full use of its relationship with cutting tool supplier WNT (UK) (0800 073 2073), as the application of modern cutting tool techniques has been central to many of the improvements made. "About three years ago, industry was moving forward at a very fast pace and, to be honest, we were finding it difficult to keep up with the increase in demand," says Mr Smith. "We were faced with a choice of replacing a number of our existing machine tools in order to increase productivity, a route that would have been prohibitive, due to the cost." That assumption was based on the belief that its existing machine tools could not fully exploit modern cutting tools. But, with the support of WNT (UK), the company did investigate tooling as a first course of action. "Utilising the machines we already had by investing in new tooling, and the increases in feeds and speeds that we achieved, made a significant impact on improving our manufacturing capacity, workflow and delivery performance before we even had to consider new machine tool investment," says Mr Parfett. "The added bonus was that eliminating many operations by using the next generation of tooling – such as WNT's HPC milling cutters, the multi-function Eco-cut tools and driven toolholders – opened up many more machining possibilities, reduced non-cutting and work in progress time, as well as eliminating many second operations, reducing the overall number of tools and generating additional savings." By attacking the problem this way round, Instrument Machining Service was then in a much better position to assess just which machines needed to be replaced and the subsequent capital expenditure was much more focused. And the cutting techniques that the company tested on its older machine tools are now being put to even better use on its new ones. An example of how this co-operation worked at Instrument Machining Service is the use of WNT (UK)'s HPC solid carbide end mills on a machine that is 20 years old. The machine has a maximum 4000 rpm/min spindle, and the prospect of running the latest in solid carbide cutting tool technology was a daunting one. However, with support from Adam Cross, WNT (UK)'s technical sales engineer for the area, this machine is now achieving feed rates of 0.75 m/min, while improving surface finish, maintaining tolerance and only taking a single pass. The company has subsequently maintained and gained business. For example, a low-volume part that was proving difficult to machine, and as a result was sub-contracted by IMS, was brought back in-house when volumes increased and the sub-contractor demanded an increase per part. With tooling technology revisited, and by working with WNT (UK) and Mr Cross, the cycle time on these parts was reduced by 66 per cent. This one-time problem component is now a profitable part for the business. To keep this cutting tool technology under control, Instrument Machining Service has now taken the next step and installed a WNT TooloMat tool vending system. Elsewhere, a leading Scotland-based supplier of high technology sub-assemblies for use in the oil industry has made significant savings by utilising helical interpolation thread milling with single point tooling supplied by Horn, via Scottish distributor Peter Campbell Sales. On one job alone, the switch from multi-flute inserts to a Horn (01425 481800) Supermini Type 105-derived special tool to produce 0.25 inch UN threads saves £1,000s per year, due to longer tool life and reduced insert cost. In addition, superior thread quality, as defined by improved parallelism and cleaner thread profiles, has virtually eliminated rework requirements. PART OF THE WHOLE This application was one of a wider programme of conversion to single point thread milling. The end user company operates in a sector where quality is critical, machining substantial components from materials, such as 420 grade stainless, 4140 stainless and Inconel 718, using a variety of high quality CNC machine tools. These alloys represent a machining challenge in any circumstance. However, the problem is often compounded by difficulties relating to accessing the location of the designated feature. In the case of the 0.25 inch thread instanced above, the feature is machined in the front face of a shoulder situated about 200 mm from the front face of the component. This demands use of a lengthy extension bar to present the threading tool to the bore, which is itself counterbored at the entrance. Instrument Machining Service's production engineer comments: "With the multi-flute tool that we used previously, there was a cumulative rigidity problem, because of the way that the tool interfaced with the holder. This led to quite rapid wear of the tool, which compromised the quality of the thread." The solution, introduced by Horn, utilises a purpose-built long length toolholder. This is produced to the maximum cross section that can still clear the spigot and access the bore. The bar is tapered at the 'business end' to a short tool holder section. The Type 105 thread milling insert clamps directly to the holder, using a single central screw. Torque is transmitted by precision machined matching interfaces on the tool holder nose and insert back designed so that the assembly acts as a solid entity. The tool assembly is more rigid, while the cutting forces developed by the single point cutter are lower than those for a multi-flute cutter, reducing the risk of vibration. "The Horn set-up provides a more consistent high quality thread, which eliminates the need for rework. Moreover, tooling costs are significantly lower," says the sub-contractor. Image: Threads required in the face of a shoulder are set 200 mm back from the component's front end First published in Machinery August 2009