38 FASTENERS AND JOINING/SEALING/SEPARATING
➠
welding burn off the zinc coating and adversely affect both the joint strength and the subsequent corrosion resistance of the steel. For these reasons, there is a
resurgence in interest in brazing. Whereas welding requires the temperature to be raised to the melting point of the parent metal, brazing takes place at lower temperatures that minimise damage to the zinc coating and do not change the metallurgy of high- and ultra-high-strength steels. A popular way to apply the
braze is by using Mig equipment. Generally very similar if not identical to the Mig power source, controller and torch that would be used for Mig welding, Mig brazing sets are available in formats for use in both automated manufacturing environments and manual operations. Manual Mig brazing is widespread in automotive body repair shops, where it is important to avoid using traditional repair techniques on high-strength and ultra-high-strength steels. Typically the brazing wire will be a copper-silicon alloy, and the process has the added advantage of not
Steel for future vehicles
choice for lightweight vehicles, but the world’s steel producers are arguing that steel offers good combination of strength, stiffness, weight and cost, as well as being easy to recycle. The WorldAutoSteel organisation also claims that steel produces five to 15 times less emissions than other materials used for reducing weight in vehicles. WorldAutoSteel has undertaken
A
a number of projects to examine the potential for steel to be used in lightweight vehicles, including the Ultralight Steel Auto Suspensions (ULSAS) Programme, Ultralight Steel Auto Closure (ULSAC) Programme, Ultralight Steel Auto Body (ULSAB) Programme and Future Steel Vehicle (FSV) Programme. By August 2008 the FSV Programme had produced styling sketches based on the packaging studies initiated in the Phase I research. The Programme is considering four technical
luminium and composite materials may appear to be the obvious
vehicle’s life cycle. The FSV’s architecture will feature
specification options for the proposed year 2015-2020 vehicle: electric (EV) and plug-in hybrid electric (PHEV) vehicles for four or more passengers; and plug-in hybrid electric (PHEV) and fuel cell (FCV) vehicles for five-passengers. It is intended that the flexibility of powertrain component packaging, coupled with the qualities of AHSS (advanced high-strength steel), will enable these vehicles to maintain current and future consumer expectations for interior comfort, while significantly reducing greenhouse gas emissions throughout the
www.engineerlive.com
the latest AHSS grades from around the world, enabling the total mass of the vehicle to be reduced without sacrificing safety or packaging requirements. As the FSV builds on the results of the ULSAB Programme, it is worth noting that more than 90 per cent of the ULSAB structure is manufactured from high-strength and ultra-high-strength steels (Fig. 3). Spot welding was used to join the majority of the parts, with the hydroformed side roof rails laser-welded to the adjacent structures and the rails in the front end structure also laser-welded. Given the extensive use of high-strength and ultra-high-strength steels, as well as the use of laser welding – which cannot be readily reproduced in repair facilities – it seems likely that Mig brazing would be needed to carry out repairs to vehicles adopting the principles promoted by the ULSAB and FSV Programmes. n
Fig. 2. Versatile and compact, the Murex Tradesmig 140-1 unit is suitable for light-duty welding and Mig brazing tasks in workshops or on site.
needing a flux. Special features recommended for the welding equipment include grooved wire feed rollers and a soft lining in the cable between the feeder and the torch. Pure argon is often used as the shielding gas to maintain a stable arc. The best results tend to be achieved with a synergic welding machine with a facility for pulsed Mig brazing, giving a combination of good speed, high strength and a finish that requires little or no dressing (Fig. 1). Unlike with welding, it is necessary to have a small gap between the components being joined so that the molten braze can penetrate by means of a capillary action. Manufacturers of welding
equipment are now actively marketing equipment as being capable of Mig brazing. For example, the Murex Tradesmig
140-1 unit weighs just 25kg and is suitable for light-duty tasks in workshops or on site (Fig. 2). Operating from a single-phase 230V supply, the machine can be used for brazing and also welding with conventional solid wires and self-shielding cored wires. n
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84