Off-line programming opened up a bottleneck

When toolmaker J Muscroft Engineering decided to invest in a high speed, hard metal machining capability, the company quickly found its existing CNC programming facilities were inadequate.

When Sheffield precision toolmaker J Muscroft Engineering decided to invest in a high speed, hard metal machining capability, the company quickly discovered that its existing CNC programming facilities became a major bottleneck.

However, as a result of installing EdgeCAM, the computer-aided manufacturing system from Pathtrace of Reading, the company has increased its business.

And, with the ease and speed of use of EdgeCAM, Muscroft is now able to generate highly reliable program data and offer key customers a very rapid turnaround on the manufacture of forging dies.

As these dies can now be machined directly from pre-hardened materials, lead times are shorter and the machine shop is now able to operate round the clock.

Technical director Neil Griffiths reflects: "We began to experiment with high speed machining a few years ago, using a spindle speeder on a conventional, modern machining centre.

While it was relatively successful it did achieve the objective of proving the process as the foundation to invest in two 'purpose-built' high speed machining centres.

We can now process hardened materials up to HRC 65 which has attracted quite a lot of interest from local companies.

This in turn, increased our part programming workload which created a bottleneck situation forcing us to look for a more up-to-date system." As word got around the forging industry, enquiries were received from a number of industry sectors that led to a well-known manufacturer of hand tools becoming a major customer for Muscroft's services.

Although the company has its own toolroom, the very fast turnaround and quality of finish capability from its high speed machining venture has proved to be an important factor in the work being placed with Muscroft.

"We looked at a number of different programming systems, beginning with a visit to MACH 2000 with follow up demonstrations at our factory." Neil Griffiths recalled: "Pathtrace performed a very good demonstration and the capabilities of the system, as a whole, were impressive.

The proximity to Sheffield of the Pathtrace training and technical centre in Wakefield also weighed in our decision to purchase." Muscroft has installed EdgeCAM Mould and the Advanced Surface Machining module that take data from both paper drawings and by electronic transfer from Client's CAD files supplied via E-mail.

When paper drawings are provided, EdgeCAM's integral drafting facilities are brought into use.

Muscroft normally undertakes original manufacture but also provides a re-cutting service for pre-forming and finishing dies.

Cavities are machined in a variety of materials, such as H20, P20, D2 and D3.

A typical set of double impression tools normally needs eight cavities to be machined.

Cavity tolerances are fairly tight, typically +0.040mm to ensure reliable assembly of the forged components with subsequent near net-shape with minimal need for machining.

Prior to machining the cavities, all alignment holes are produced in the soft state and the prepared blank is then heat treated and ground.

According to Neil Griffiths: "The big advantage of using EdgeCAM is the combination of rapid program preparation with the added ability to check that the cavity to be machined is the one we originally set out to program.

That capability gives us the confidence to commit to lights-out machining of die cavities which has made a huge difference to our productivity and overhead recovery." He continued: "One important feature to us is how accurately EdgeCAM will predict cycle time.

This allows us to organise ourselves because program run time for these parts can often be between eight and 14 hours which makes them an ideal overnight or a weekend job.

In fact, it's usually the case that we prepare the program and set the job up during the day then follow on with the machining.

The machines are equipped with monitoring and modems which enables alarm generation if anything goes wrong and our programmer can put in a telephone call at any time to determine how far through the process the program has run." Most programs for hard metal machining are developed as a suite of four cycles.

Machining begins with a fast line and pre-roughing cycle, taking about 90 minutes using a 25mm cutter.

This is followed by a 12mm cutter for the pre-roughing phase and generally by a two hour roughing cycle using a 6mm cutter.

Pre-finishing operations using a 4mm cutter, can take up to 10 hours, and final finishing is carried out with a small 1mm to 2mm diameter cutter.

Depending on the complexity of the die form, this can take between 10 and 14 hours.

Cutting data for the finishing operation involves a spindle speed around 16,000 revs/min with a 500mm/min feed.

Step-over is normally maintained at four per cent.

With this speed and feed relationship Muscroft has found it can maintain a very high standard of finish with the added advantage of eliminating the very costly finishing process.

"EdgeCAM is now an integral part of our die manufacturing process," Neil Griffiths remarked.

"The system is set up to automate certain areas of the programming process, such as our preferences for tooling and machining strategy.

Likewise, we've been able to optimise the post processors for our machine control systems using EdgeCAM's Code Wizard.

As well as manufacturing new dies, we do a lot of re-cutting and the availability of the archived programs though EdgeCAM makes this a very straightforward exercise.

Even though some programs are quite lengthy, the system is able to generate the toolpaths very quickly and with EdgeCAM DNC links to the machine controls, program transfer is also fast." The company reports having received good support from Pathtrace following its training courses at Wakefield and three programmers have now been trained in the use of EdgeCAM.

"So far we've been very impressed with the performance of EdgeCAM and its support for our investment in machine tools," Neil Griffiths concluded.

"It makes it relatively easy for us to produce forging die work and offer a very competitive turnaround.

We feel that the combination of our high speed machining capability with EdgeCAM means that we are well placed to confidently offer the service to other toolrooms and mould makers.

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