Heavy machine shop revises cutting strategies

An example of a tool supplier working closely with a heavy machine shop is the development a negative rake cutter body with a non-standard insert that provides multiple cutting edges.

When you are machining some of the largest castings ever produced, it pays to have cutters, and a tooling supplier, that deliver on their promises.

Sheffield-based heavy engineering company Davy Markham and tooling supplier Ceratizit are developing a partnership that is delivering just that.

Faced with machining castings weighing several hundred tonnes, Davy Markham regularly confronts what it describes as individual problems due to the unique components that it comes across in its day-to-day business of sub-contract machining of heavy castings for large press components and the steel rolling mill industry.

Most recently, it completed the machining, from a black foundry condition, one of the world's largest single piece casting, weighing 350 tonnes, to finish tolerances in the region of just a few microns.

As can be imagined, the tooling element of work of this scale is vital to Davy Markham's success and, given the value of the raw casting, let alone the finished item that may have been subjected to more than 1000h of machining, there is often a reluctance to change.

This has driven Davy Markham to reassess its tooling usage and, in recognising the importance of reliable, repeatable cutting tools to its business, The company has implemented sophisticated stock control and maintenance procedures to ensure that the correct tooling is always available.

As part of that process it is working closely with Ceratizit to re-examine its entire tooling requirement in order to ensure optimum performance.

This also extends to working alongside its casting partner and fellow Ceratizit customer, Sheffield Forgemasters.

"Heavy industry is often viewed as very traditional and reluctant to change," said Kevin Parkin, Davy Markham's managing director.

"However, we had to make these changes in order to compete with low-cost economies around the globe.

Happily, the changes we have made are all paying off.

In the past 18 months we have focussed our efforts on being a customer-facing business and have implemented a 100% on-time delivery programme to ensure that we continue to win repeat business.

This strategy has created a full order book for the next 12 months." He said: "Crucial to this strategy are the partnerships that we have with our suppliers.

In the past we have had what can be described as passive relationships with tooling suppliers.

What we now have with Ceratizit as a partner is a very professional relationship and we definitely see them as a partner in our business." One of the first areas that Ceratizit investigated was the finish milling of large castings.

This particular challenge was one that required confidence and trust on both parties, as the components being machined are not something that can be 'experimented' on.

"Initially we saw an opportunity to develop the existing process," said Adrian Eagle, Ceratizit's Cutting Tool Account manager.

"The original milling cutters were designed as a double negative cutter, which is not ideal for a finishing operation.

Therefore, we designed a cutter with a 45 deg approach angle and a positive rake.

The effect this had was to improve cutting data on the 250mm diameter cutters dramatically.

The feed rate was immediately increased from 400mm/min to 1200mm/min, with the potential to take this even higher.

A typical semi finishing cut at Davy Markham to a depth of 6-8mm, and then a final finishing cut of 0.1mm to achieve the exacting tolerances required, using the same cutter brings into perspective the performance of these cutters.

The main restrictions on feedrates are related to guarding and swarf collection both of which have proven to be to be an engineering challenge on the large ram borers located on a huge bed plate measuring 34.5m x 14.7m As an interim compromise, the Company has employed additional labour to keep the machine bed clear of swarf.

Risk assessments and PPE improvements have been implemented to protect the operator.

Once the finishing cutters had proved their worth, Ceratizit was tasked with investigating the roughing operations.

"The biggest challenge facing Ceratizit in this area was one of consistent metal removal," said Parkin.

"Again, due to the scale of the castings being machined we are often faced with sand inclusions and differential hardness of the cast material.

We have worked closely with several research organisations to attempt to eliminate these problems but to no avail, as yet.

Therefore, it is down to the cutting tool design to cope with these inherent problems.

Any tool design has to be able to absorb these material changes without the requirement to adjust speeds and feeds." To solve this particular problem Ceratizit has developed a negative rake cutter body that uses a non-standard insert that provides multiple cutting edges, which is a major cost-benefit.

As with the finishing cutters swarf removal is a major issue, and Ceratizit has invested time and effort into specific insert geometry designs to ensure that chipbreaking is achieved in a controlled manner.

This is achieved by the specific land and edge preparation undertaken on the inserts.

"Improving cutting tool performance is a major factor in our drive to deliver our Total Punctuality Concept, whereby everything we do is delivered on time - every time," said John Watson, Davy Markham's production manager.

"With machining times running to over 1000h on some components and the possibility of numerous components being machined simultaneously we have to monitor closely the scheduling of workloads on a daily basis.

Cycle times are now broken down into manageable segments to allow daily monitoring of each process cycle time thus giving greater awareness and flexibility, and by dramatically improving cutting tool performance we are much better placed to meet customers' delivery requirements.

When it can take days simply to turn a casting over to machine a different face, time saved in machining can prove vital." * About Davy Markham - Davy Markham has a long history going back to the early 1800s in the design, manufacture, fabrication and machining of heavy and complex engineering components and assemblies.

Many of its facilities are unique within Western Europe, in terms of capacity and capabilities.

The company combines its expertise in hydraulics, controls, engineering, installation and servicing, along with the ability to handle individual structures weighing up to 350 tonnes, to provide a service to a wide range of heavy industries, including steel mills, mining, bridges, control towers (T5 Heathrow), large press components and the power generation sector.

Having witnessed many ups and downs through this history, Davy Markham hired the services of Kevin Parkin a proven turnaround expert to return the business to profitability and secure its future.

During the last twelve months Parkin and his fellow associate Duncan Hay (the finance director) have successfully turned the business and it now has a full order book and a very positive and profitable future.

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