Tailor-made tool inserts
Aachen, Germany-The Fraunhofer Institute for Laser Technology (ILT; www.ilt.fraunhofer.de) has qualified two rapid manufacturing techniques for the production of customized tool inserts made of gradient materials, or combinations of materials, for use in toolmaking: laser cladding of blanks with gradient coatings, and generative manufacturing of tool inserts made of a combination of materials using selective laser melting (SLM).
The mold cores in injection molding tools must be able to dissipate heat from the plastic quickly in order to minimize cycle times and guarantee reliable demoldability. Copper is a suitable material for such purposes, but its resistance to wear and corrosion are unsatisfactory for most applications. Therefore, Fraunhofer ILT uses laser cladding to coat the mold cores with a graded film on steel base (see Figure 1). The gradient coating provides a degree of wear resistance comparable to that of tool-quality steel.
Gradient materials also can offer significant advantages to manufacturers of die-cast tools. Researchers also have demonstrated the construction of tool inserts with a stainless-steel core covered with a wear- and corrosion-resistant steel alloy applied by means of laser cladding.
SLM is employed to manufacture mold inserts with complex tempering channels. By building up the part layer by layer on the basis of CAD data, it is possible to produce any type of complex, hollow structure that cannot be produced using conventional manufacturing techniques. This SLM process is capable of processing commercially available metallic production materials in powder form. This enables injection tools to be manufactured directly for series production. The near-net-shape tempering channels enable the tool to cool off rapidly, which not only reduces manufacturing cycle time but also improves the quality of the plastic products.
An alternative technique being developed in collaboration with the Foundry Institute at RWTH Aachen involves mold inserts that are manufactured from a combination of materials. SLM is used only to build up the hollow shell of the mold insert (see Figure 2). The empty space inside it is then filled with a different material by casting. This results in a product where, for example, the outer core is composed of a wear-resistant tool-quality steel, and a highly thermally conductive material such as copper or aluminum alloy is used as the casting material.
The advantage is that the mold core can be cooled evenly (due to the excellent thermal conductivity of the core) and requires few cooling channels or none at all, which represents a significant reduction in the time needed for construction.
For more information, visit www.ilt.fraunhofer.de.
Laser marking faceplates
Luxembourg-The Elster Group, a manufacturer of high-quality integrated meters to the gas, electricity, and water industries, employs more than 8500 and has operations in 38 countries. Many of the company’s metering devices require marking a faceplate with various texts and graphics, including logos, model and serial numbers, and machine-readable barcode data. The faceplates are made of anodized aluminum with some areas silk-screen coated. The company uses a laser to ablate the coated area providing permanent marks with high contrast and good reliability. Other marking fields may require direct marking into the base aluminum. Such marking creates good contrast through a thermal process created by the high average and peak power of the beam which darkens the aluminum through oxidation. In addition, the laser used in the production meter plate marking system can perform engraving of the aluminum to a depth of several thousands of an inch.
The laser marker for this application had to be flexible enough to mark both surfaces with good contrast and at a speed to match the high-volume production requirements for these devices. To meet the contrast and speed requirements, Elster chose a Rofin-Baasel (Boxborough, MA; www.rofin.com) RSM 20E Nd:YVO4 diode-pumped laser operating at a wavelength of 1064 nm and 20 watts.
This laser is activated by a fiber-coupled diode pack, which has an average operating life of up to 30,000 hours. On a two-shift, five-day-a-week schedule, the diode packs will operate for up to about eight years. Laser parameters to enable marking of meter faceplates consist of laser power, pulse rate, and pulse width. The laser output beam is expanded to achieve the desired minimum focal spot and energy density. The 160mm flat field lens will achieve a marking field of 150mm diameter. Changing the laser or focusing variables will result in a different effect on the aluminum plate. Reducing the pulse rate increases the peak power, which increases the depth of the mark. Increasing the pulses rate will produce a smoother mark but can also increase the marking speed. Changing the focus position will change the focus spot diameter, which will reduce the power density of the laser.
Reportedly, preventive maintenance for the laser is minimal and consists of periodically replacing the cooling water and filter. The diode pack is not an item that Elster will need to keep in stock. The cover glass plate protecting the flat field lens requires periodic wiping with an appropriate lens cleaning cloth and isopropyl alcohol. Maintenance of the mechanical transport system for the tags is also minor with the most important task being to remove the accumulation of a small amount of dust from the plate transport mechanism.
The turnkey CDRH Class 1 system marks nameplates utilizing an automated handling system for several models of nameplates. The workstation also houses the laser control components, automated nameplate handling system, barcode reader/verification system, and all necessary power distribution and control components. Interchangeable cassettes hold a minimum of several hundred nameplates. The cassettes automatically signal the marking system to select the proper program, which updates serial numbers and other pertinent information. A color sensor verifies the correct nameplate color during auto-loading. The system also contains a reject station.