- Email: [email protected]
Sandia creates wear-resistant diamond coating
MIM provides for thought A
food
-
fter its long struggle for market acceptance, eta1 injection moulding (MIM) may soon find itself eating from the high table following its success in trials at a leading German manufacturer of table and kitchenware. Wiirttembergische Metallwarenfabrik (WMF), one of Germany’s largest producers of cutlery, utensils and other kitchen products, will shortly begin marketing a designer demitasse spoon produced via the MIM route. Initially, the part will be produced by a commercial MIM parts manufacturer in France, although it follows extensive in-house research and feasability testing at WMF. The company’s adoption of MIM stems from the efforts of its R&D department to explore the possibilities of a range of production processes to economically produce parts with unusual, and technically demanding, features.
MIM advantages In researching MIM, WMF found that it could greatly reduce the number of steps used to produce cutlery in comparison with its conventional process. Indeed, in the initial manufacturing stage MIM requires only three steps (injection moulding, debinding and sintering) compared with the nine steps used in the existing production route (cutting, rolling, fine blanking, degreasing, grinding, washing, annealing, greasing and coining). In addition to the cost savings from reducing the number of production steps, MIM also offers design advantages as it is better able to meet certain requirements such as round cross-sections, revolving grooves, concaveconvex figures and large (for the cutlery world) diameters. Further, as the MIM route
only requires one set of tooling, automation is facilitated. Other advantages, compared with competing routes, are that MIM produces solid parts and is a near-net shape technology.
Quality characteristics To be suitable for use in cutlery, MIM parts must be able to satisfy a number of mechanical and quality requirements. In particular, a very high surface quality is required, while corrosion resistance and strength parameters are also important. WMF made extensive trials of 316L stainless steel test parts to test the capability of the MIM route to meet these demands. Although the lower density of the MIM parts, 0.08 g.cm-3 below that of the conventional parts, did impact on the properties they were still sufficient to meet the application requirements. Strength and hardness are lower because of the reduced hardening effect during coining, but still meet the required deflection under load parameters. The parts also passed dishwasher tests for corrosion resistance. One problem area for the MIM route was matching the surface finish of parts produced via the conventional route. The required shine can be achieved, but requires a little more polishing time, which is a source of some extra cost compared with the traditional route.
spoon in this cutlery range from WMF:
Materials
While the production advantages point to MIM being an excellent route to cutlery production, WMF encountered a major barrier to its adoption. As with other potential MIM applications, the much higher raw material cost - about ten times that of the sheet metal that is normally used - pushed the total production costs to beyond that of most competing methods. Material costs alone mean that the use of MIM will be restricted to designer cutlery models. If this problem can be solved, it opens up the possibility of a large market for MIM - a factor that should give the industry plenty of food for thought.
7.98 0.3 210 0.1 OK
Density (g.cme3) Roughness (pm) Hardness (max, HVIO) Deflection under load* (mm) Corrosion resistance* _-.___-.~---___-____.___. *prEN 28442 - the European
standard
expense
7.91 0.4 160 0.4 OK
I
.__~.
MPR June 1998 11
ture, an amorphous carbon film with a high percentage of diamond-like bonds but with high initial stress. “Then,” says Friedmann, “we discovered that when the deposited material is heated, these films lose their stress, yet retain their diamond-like properties. In contrast, amorphous diamond films that contain hydrogen convert to graphite upon heating.” The process seems to involve short-range bond rearrangement as opposed to long range atomic migration which occurs in many other materials. “The surprising thing is that the hardness seems to be unaffected by the subtle rearrangements,” says Friedmann.
Cutting
tool uses
With regard to powder metallurgical (PM) applications, Friedmann says the coating would be suitable for tool bits. He says the material is hard and stiff and in the demonstrated 4-10 pm thick-
SLOT
ness range is suitable for many tool coating applications. Further development is needed to realise this promise, however, such as efforts to increase the deposition rate. From a technical standpoint, the coating is carbon, and it will suffer from the same limitations of diamond in terms of machining ferrous metals. It is oxidation resistant up to -4OO”C, and in inert environments will hold up to -800°C where it converts to nanocrystalline graphite. Also, the coating process is line of sight, making it difficult to coat complex parts. A current limiting factor is the need to heat treat the substrates in order to relieve the stress. “We build up a thick layer by depositing stressed thin layers, and annealing after each deposition to relieve the stress,” Friedmann says. “Layers deposited above -200°C are graphitic and soft; therefore, the substrate must be cooled
HEATER
back down near room temperature before further deposition. The time required to build up a thick coating is then limited by the heat treating process. Friedmann says an obvious means of speeding up this process would be to surface anneal (e.g. a laser pulse) to heat only the surface of the part, thus limiting the thermal budget and reducing the time to cool the part back to room temperature. Research into the coating has been funded by Sandia’s Laboratory-Directed Research and Development programme for leading-edge, proof-of-principle research, while DOE funds are used to continue development. Sandia is now actively seeking partners for involvement with the project, both for cooperative research opportunities and licensing. Contact: Tom Friedmann Sandia National Laboratories; Tel: +l-505-844-6684; Fax: +l-505-844-1197; E-mail: [email protected]
REPRINTS HEILP SALES AND REDUCE COSTS Promote your company and save .:..: :: money by having reprints of an i.. ‘i:; article or whole page a,dvertisement :... :,. :., that appears in this issue.
: :::
Capacities: 4.5 and
The Slot heater preheats the powder and can be fitted to all press types.
For further details and quotations contact: .G,. .:. .:: ..:,..: ,ji.; g:,; Elsevier Advanced Technology Y. P.O. Box 150, Kidlington, 3 .::: OXFORD OX5 lAS, UK. .j Telephone Number: [44] (0) 1273 423512
MPR June 1998 13
food
-
fter its long struggle for market acceptance, eta1 injection moulding (MIM) may soon find itself eating from the high table following its success in trials at a leading German manufacturer of table and kitchenware. Wiirttembergische Metallwarenfabrik (WMF), one of Germany’s largest producers of cutlery, utensils and other kitchen products, will shortly begin marketing a designer demitasse spoon produced via the MIM route. Initially, the part will be produced by a commercial MIM parts manufacturer in France, although it follows extensive in-house research and feasability testing at WMF. The company’s adoption of MIM stems from the efforts of its R&D department to explore the possibilities of a range of production processes to economically produce parts with unusual, and technically demanding, features.
MIM advantages In researching MIM, WMF found that it could greatly reduce the number of steps used to produce cutlery in comparison with its conventional process. Indeed, in the initial manufacturing stage MIM requires only three steps (injection moulding, debinding and sintering) compared with the nine steps used in the existing production route (cutting, rolling, fine blanking, degreasing, grinding, washing, annealing, greasing and coining). In addition to the cost savings from reducing the number of production steps, MIM also offers design advantages as it is better able to meet certain requirements such as round cross-sections, revolving grooves, concaveconvex figures and large (for the cutlery world) diameters. Further, as the MIM route
only requires one set of tooling, automation is facilitated. Other advantages, compared with competing routes, are that MIM produces solid parts and is a near-net shape technology.
Quality characteristics To be suitable for use in cutlery, MIM parts must be able to satisfy a number of mechanical and quality requirements. In particular, a very high surface quality is required, while corrosion resistance and strength parameters are also important. WMF made extensive trials of 316L stainless steel test parts to test the capability of the MIM route to meet these demands. Although the lower density of the MIM parts, 0.08 g.cm-3 below that of the conventional parts, did impact on the properties they were still sufficient to meet the application requirements. Strength and hardness are lower because of the reduced hardening effect during coining, but still meet the required deflection under load parameters. The parts also passed dishwasher tests for corrosion resistance. One problem area for the MIM route was matching the surface finish of parts produced via the conventional route. The required shine can be achieved, but requires a little more polishing time, which is a source of some extra cost compared with the traditional route.
spoon in this cutlery range from WMF:
Materials
While the production advantages point to MIM being an excellent route to cutlery production, WMF encountered a major barrier to its adoption. As with other potential MIM applications, the much higher raw material cost - about ten times that of the sheet metal that is normally used - pushed the total production costs to beyond that of most competing methods. Material costs alone mean that the use of MIM will be restricted to designer cutlery models. If this problem can be solved, it opens up the possibility of a large market for MIM - a factor that should give the industry plenty of food for thought.
7.98 0.3 210 0.1 OK
Density (g.cme3) Roughness (pm) Hardness (max, HVIO) Deflection under load* (mm) Corrosion resistance* _-.___-.~---___-____.___. *prEN 28442 - the European
standard
expense
7.91 0.4 160 0.4 OK
I
.__~.
MPR June 1998 11
ture, an amorphous carbon film with a high percentage of diamond-like bonds but with high initial stress. “Then,” says Friedmann, “we discovered that when the deposited material is heated, these films lose their stress, yet retain their diamond-like properties. In contrast, amorphous diamond films that contain hydrogen convert to graphite upon heating.” The process seems to involve short-range bond rearrangement as opposed to long range atomic migration which occurs in many other materials. “The surprising thing is that the hardness seems to be unaffected by the subtle rearrangements,” says Friedmann.
Cutting
tool uses
With regard to powder metallurgical (PM) applications, Friedmann says the coating would be suitable for tool bits. He says the material is hard and stiff and in the demonstrated 4-10 pm thick-
SLOT
ness range is suitable for many tool coating applications. Further development is needed to realise this promise, however, such as efforts to increase the deposition rate. From a technical standpoint, the coating is carbon, and it will suffer from the same limitations of diamond in terms of machining ferrous metals. It is oxidation resistant up to -4OO”C, and in inert environments will hold up to -800°C where it converts to nanocrystalline graphite. Also, the coating process is line of sight, making it difficult to coat complex parts. A current limiting factor is the need to heat treat the substrates in order to relieve the stress. “We build up a thick layer by depositing stressed thin layers, and annealing after each deposition to relieve the stress,” Friedmann says. “Layers deposited above -200°C are graphitic and soft; therefore, the substrate must be cooled
HEATER
back down near room temperature before further deposition. The time required to build up a thick coating is then limited by the heat treating process. Friedmann says an obvious means of speeding up this process would be to surface anneal (e.g. a laser pulse) to heat only the surface of the part, thus limiting the thermal budget and reducing the time to cool the part back to room temperature. Research into the coating has been funded by Sandia’s Laboratory-Directed Research and Development programme for leading-edge, proof-of-principle research, while DOE funds are used to continue development. Sandia is now actively seeking partners for involvement with the project, both for cooperative research opportunities and licensing. Contact: Tom Friedmann Sandia National Laboratories; Tel: +l-505-844-6684; Fax: +l-505-844-1197; E-mail: [email protected]
REPRINTS HEILP SALES AND REDUCE COSTS Promote your company and save .:..: :: money by having reprints of an i.. ‘i:; article or whole page a,dvertisement :... :,. :., that appears in this issue.
: :::
Capacities: 4.5 and
The Slot heater preheats the powder and can be fitted to all press types.
For further details and quotations contact: .G,. .:. .:: ..:,..: ,ji.; g:,; Elsevier Advanced Technology Y. P.O. Box 150, Kidlington, 3 .::: OXFORD OX5 lAS, UK. .j Telephone Number: [44] (0) 1273 423512
MPR June 1998 13