Forging dies produced in hours instead of days

In 2000, Dudley Die Forgings (DDF), embarked on a £1m project to establish a CNC die shop at its Holly Hall works, in Dudley, near Birmingham. The acquisition of a Renishaw Cyclone scanning system was instrumental in setting up a forging die CAD database on which to establish CNC die machining practices. The Renishaw Cyclone machine and CNC die machining have subsequently reduced factory lead times for hammer forging dies. The project was carried out with the support of C & W Production Engineering, based in West Gorton, Manchester.

"Our aim was to replace the old die shop which relied on traditional copy-milling and manual die finishing," explained CNC Die Shop Manager, Lee Wardle. "We have established the new CNC die shop, and have considerably reduced factory lead-times for producing new die sets and reconditioning worn ones.

Crucial to the success of the CNC die shop was the scanning of existing tools and patterns. Most of this 'reverse engineering' work has now been completed, " said Lee Wardle. "Our use of Cyclone is now concentrated on the day-to-day scanning of worn tools. Meanwhile, we continue to develop our suites of CAD/CAM software."

DDF negotiated a CNC die machining turnkey package with C&W, which included Renishaw's Cyclone, two Correa CF17D CNC bed mills for roughing and a Deckel Maho 103V CNC machining centre for high speed finish milling. As part of the package, Delcam supplied the CAD/CAM software suite including CopyCAD for reverse engineering. "We started the CNC die shop project in August 2000," said Lee Wardall, "and anticipate a total investment of some £3/4-1m."

The first CNC bed mill and Cyclone machine were delivered to C & W during the early months of the project. DDF's die shop personnel undertook training at C & W, which included the scanning of existing patterns. The equipment was then delivered to Holly Hall in January 2001, where it was installed in a refurbished, dedicated building. Within a month the other bed mill was installed, closely followed by the Deckel Maho machine.

"The 'step-by-step' approach gave us time to get acquainted with the scanning and CAD/CAM software and establish CNC die machining routines," said Lee Wardle. "We began to see an immediate impact on die manufacturing lead-times. For example, it used to take at least one week to produce a set of 'finisher' dies to produce an automotive 'wishbone' suspension arm forging. Now it takes us 10 hours." A 'finisher die' is the last drop-stamping operation which sets final dimensions, and is therefore the most critical for dimensional accuracy.

The Renishaw Cyclone machine is located in the CNC die shop and is linked, via a local area network (LAN), with the workstations running the Delcam software. Substantial roller tables have been located either side of Cyclone to handle the larger dies - DDF operates drop hammers and dies can have lengths of up to 1500 mm. The practice with such dies is to establish datum lines and scan in sections. For example, dies to produce the radius arm forgings for the Land Rover Discovery vehicle, need two or three datum positions. The corresponding sets of scanned data are then merged in the Delcam CopyCAD software.

"Our practice with most new jobs is to produce 3D die set models in CAD and generate CNC machining data from CAM. When a worn die set is returned from the forge, it is scanned on the Cyclone a job which can take up to 24 hours for a large die and the as-measured data is compared with the original CAD model," explained Lee Wardle. "The comparison highlights the wear areas; we can then replace the original die material with that of a better quality."

General die reclamation practice is to gouge out worn areas using arc-air welding, then 'flood-weld' the cavities. DDF uses a subcontractor to do this. Flood-welding is a high amperage, automatic MIG-welding process, in which the die has to be preheated before the cavities are filled 'or flooded' with weld metal. After flood welding, new die cavities are machined in DDF's CNC die shop. Die materials used at DDF are mostly Electem A or B of 86 tonf/in² and mid-40s Rockwell hardness. Flood-welded material is nearer 50 Rºc with a tensile strength of 90-95 tonf/in².

So far, DDF's CNC die shop has used CNC three-axis die milling, but is about to embark on four-axis (3+1) milling. The company uses roll-forming machines on some jobs to produce pre-forms prior to forging. The tools used in roll-formers are akin to a set of mill rolls, but with the pre-form impressions milled into the rolls' peripheries. These were formally produced by a combination of copy-turning and copy-milling. Using Cyclone, initially to scan existing patterns and templates, will establish the CAD/CAM routines for generating the CNC programs to be used in the Deckel Maho CNC machining centre. Thereafter, pre-form roll sets will be produced and repaired using the same scanning practices as for the forging dies.

As well as drastically reducing factory lead-times, DDF is realising a considerable manpower saving. Up to 30 were employed in the traditional die shop in machining, finishing and die maintenance. The CNC die shop, including CAD/CAM personnel, employs around a dozen. The CNC machines are worked on a three-shift system, providing 24 hour coverage. However, DDF is aiming at a 24/7 operation.

"Our die making practices are now more similar to a production engineering operation," said Lee Wardle, who is relatively new to the die-making scene, as his background is in CNC production machining. DDF's investment in CNC die machining, supported by its parent holding group, Klesch & Co, has already put the company on a much more competitive footing.

Hammer forging and drop stamping capacity in the UK has already been severely reduced in the face of cheap imports, but DDF is now in the position to reverse the trend. The company offers an up-to-date die-forging consultancy, with very fast turnaround times on die design, manufacture and prove-out, and a consistent, on-time, high quality delivery of forgings.