Fastening innovations broaden the options of design engineers

Written by: Paul Fanning | Published:

A number of recent mechanical fastening and joining developments are creating new design opportunities for a variety of applications.

For instance, a new earthing stud is allowing leading automotive OEMs to achieve the triple benefits of reduced installation time and cost, guaranteed electrical earthing and a substantial reduction in part count all at once.

Developed to keep pace with the materials mixes now prevalent in advanced vehicle manufacturing, the new KSB earthing stud from Profil has already allowed several automotive OEMs to reduce the number of earthing points on top-selling vehicles from thirty down to twenty-two. But this 25% saving on parts (and associated installation costs) is only part of the story.

Because the stud is self-piercing, manufacturers are also seeing significant cost savings by doing away with the need for the expensive additional processes involved in either welding studs into place or having to drill holes and then bolt them on. Also, with material thicknesses being continually reduced in the quest for weight saving, an added advantage cited by those now enjoying all the benefits of the Profil earthing stud is that the risk of deformation in the parent material – always high with welded studs – has also been eliminated through the use of a cleaner, better mounting and installation method.

Specified worldwide by some of the biggest brands, including Porsche, Mercedes-Benz, BMW and Jaguar Land Rover, Profil’s earthing stud has proven to be ideal for fitting at the body-in-white (BIW) stage, because it is installed complete. Its flanged construction also provides a total seal against paint or other material ingress or bleed through. When the vehicle then progresses from BIW to the electrical installation process, it is a quick and simple task to remove the integral nut on each Profil earthing stud, offer up the required cable shoes to the pair of completely clean faces and then torque it down for a guaranteed earth across the lifetime of the vehicle.

KSB earthing studs are available in two versions and can be used in both steel and aluminium construction, with material thicknesses ranging from just 0.7mm right up to 4mm. Profil recommends that OEMs embrace a galvanic coating on the studs where possible. All KSB earthing studs can be installed either manually for short-run or prototyping purposes, or by bespoke, fully automated installation equipment designed and installed by skilled Profil engineers direct into production lines.

Polymers

Moving away from metal, however, igus has expanded its range of leadscrew nuts with the material iglidur E7 for trapezoidal and high helix leadscrews. This is characterised by its smooth and low-vibration operation with low loads and high speed.

“In everyday life, linear drives can be found everywhere, from camera slides to train doors, wherever precise adjustment is required,” says Robert Dumayne, dry-tech director at igus. “Leadscrew units traditionally consist of two components: the leadscrew and the associated nut. At high adjustment speeds, leadscrew nuts made of standard plastics or metallic alternatives often reach their design limits. The consequences of which are unwelcome vibration and noise.”

For this reason, igus has added the material iglidur E7 to its range of leadscrew nuts for high helix and trapezoidal lead screws. The nuts are designed specifically for high-speed applications with low loads and small installation space. Typical application examples include fully automatic coffee machines, 3D printers or even in laboratory technology.

In comparison to other leadscrew nut materials, iglidur E7 is a high-performance polymer that is self-lubricating and therefore maintenance free. The softer material reduces noise while at the same time acts as a vibration-dampening device.

The in-house wear comparison test between iglidur E7 and the igus standard material revealed that this new material offers superior performance. The iglidur E7 leadscrew nut at 135 rpm and a load of 100 N has four times higher wear resistance on a high helix leadscrew and 19 times better wear resistance on a trapezoidal leadscrew. With matching materials and geometries, the new leadscrew nuts and the patented igus dryspin high helix thread technology provide the optimum linear drive.

Another non-metal fastening solution, Fitsco Industries’ recently unveiled LiteFit plastic inserts (see picture, below) have been attracting interest from a number of medical device manufacturers, according to the company. Launched just a few months ago, the LiteFit threaded insert is a patent-pending new product, made in the UK from a type of plastic originally developed for aerospace applications in the US. Among other attributes, the material is stated to be of “exceptional hardness”, says Fitsco CEO Philip Schofield, and offers design engineers the further advantages of lightness, durability and resistance to corrosion.

However, it isn’t these attributes that has attracted attention from the medical market. For example, recent enquiries concerned both the manufacture of MRI scanners and also the patients being studied within them. In the latter case, the fact that the scanner can ‘see through’ the new Fitsco plastic inserts attracted interest because of their potential for use ‘in or on body’ applications in a variety of medical devices. A concurrent benefit, this time for the manufacturers of the scanners themselves, is the non-magnetic properties of the LiteFit material. This is seen as a key advantage in an application environment, where the reduction of metal parts is of special value.

Magnetic Resonance Imaging (MRI) scanners provide medical staff with outstanding visual presentations of the chosen sections of the human body that is being examined, but the details provided can sometimes lack absolute clarity, due to a number of factors. In computed tomography (as in CT scanners), these variations are referred to as ‘artefacts’, a term applied to any systematic discrepancy between the CT numbers in the reconstructed image and the true attenuation coefficients of the object being studied. CT images are stated to be inherently more prone to these artefacts than conventional radiographs, because the image is reconstructed from somewhere in the region of a million independent measurements.

There are said to be a number of causal factors behind the presence of these artefacts in scans, two of which are patient-based. One of them results from patient movement during the scan itself and the other is due to the presence of metallic materials or objects in or on the body of the patient being scanned. The fact that these medical scanners and x-ray devices can ‘see through’ the plastic LiteFit threaded inserts is thus cited by Fitsco as a significant advantage to medical device designers and manufacturers. Additionally, for prosthetics or ‘in body’ devices, using LiteFit threaded inserts also obviates concerns about the potential material deterioration or degradation that may occur with metal inserts.


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