Choice of Material Type
Choice of material will depend on a number of considerations including cost, sensitivity to weight, thermal properties, chemical resistance, potential exposure to corrosive influences, dielectic strength, and relative properties of adjoining materials.
Where electrolytic reaction with dissimilar metals is a possibility, consideration should be given to the use of Shimtech’s unique cadmium-plated steel LS3 variant which is prepared with a coating to both sides of each foil prior to lamination
Quality standards demanded by The Boeing Company require the use of fully coated (Type 1A) foils for use in laminated aluminum products.
If a shim is to be used in a stressed location, it is important, especially in the aluminum range, that the shim strength is similar to that of the surrounding structure.
Considerable weight savings can be achieved by the substitution of traditional metallic shim products with lighter weight, non-metallic materials. These include polyimide and carbon and glass fiber composite materials, the later generally made from pre preg cloths.
Polyimide has good physical, chemical and electrical insulation properties over a wide temperature range for use in aerospace applications and is laminated from 0.075mm (0.003”) and 0.13mm (0.005”) films. It can be backed with a solid portion made from a cotton-based phenolic resin.
Carbon and glass fiber composite materials also provide weight saving and can be produced as either solids or in peelable form. They are more expensive and less flexible than polyimide.
Having calculated the maximum variation that may result from tolerance accumulation, it is recommended that shim thickness be specified at just above that figure. A selection from the thickness table (see material selection table) could offer economic benefits since standard material is normally ex-inventory, avoiding the need for special sheets to be manufactured. Sheet thicknesses range from 0.15mm (0.006”) to 12.7mm (0.5”).
Foils ranging from 0.025mm (0.001”) or 0.1mm (0.004”) are used in the manufacture of standard shim stock and will impact on the final degree of accuracy achieved on the assembly fit. Foils of 0.05mm (0.002”) or 0.075mm (0.003”) normally satisfy most assembly demands.
Shimtech is able to provide a range of peel strengths to suit varying user preferences and application requirements, from a very light peel (at approximately 1lb per square inch of resistance), to allow easy adjustment by knife or hand, to a much stronger peel.
Sizes & Shapes
Shimtech’s standard shim stock sheet size is 610mm (24”) x 1220mm (48”), but custom sizes can be made on request. As a general rule, punched hole diameters must be twice the material thickness and the flange or remaining width similarly must be twice the material thickness. Light, single curvature forming can be achieved but double curvature forming invariably results in laminate failure.
Shimtech can supply a complete range of solid, semi and fully laminated materials that are compliant to industry standard specifications for the UK (British Standard), Europe and the USA.
These include customer-specific standard material/part number designations, as well as US military (AMS) specifications (Note: MIL-S-22499 has been superseded by AMS-DTL-22499).
We manufacture all of our own laminated material for conversion into detail parts (using a variety of processes) or for sale as sheets. Standard sheet sizes are 610mm (24”) x 1220mm (48”).
Our manufacturing systems use proprietary processes involving the application of heat, pressure and bonding agent to individual foils of material in thicknesses varying from 0.025mm (0.001”) to 0.1mm (0.004”), to produce laminated sheets.
Laminated sheets and detailed parts can be backed with solid material in various thicknesses to suit particular applications and can be supplied in a range of peel strengths.
Laminated sheet thicknesses vary from 0.15 mm (0.006”) to 12.7mm (0.5”).
We stock a wide range of material types (across three strategic inventory locations) including:-
Cadmium -Plated Steel
Polyester (PET) (1)
(1) Polyester (PET) is Mylar® peelable treated polyester film.
Other materials can be obtained on request to suit’ particular requirements. Please contact us directly for further information or with any specific enquiries you may have. We will be delighted to assist.
As the largest specialist manufacturer in the world, Shimtech can supply shims, fillers, tapers, packers, spacers, washers and gaskets to almost ever standard aerospace customer specification.
Some of the more common standards currently include:-
Since we have some of the fastest and most modern equipment available, we can provide a dependable, highly competitive source of supply whatever your requirements, whether in small, medium or high volume.
Please contact us for further information.
Shimtech’s businesses hold ship-to-line approvals covering a broad range of manufacturing processes and materials from all of the major aircraft manufacturers and many of their tier one suppliers. For a full list of the customer approvals we hold, please contact us directly.
To find out more about our quality management systems or to view copies of accreditation certficates, please click here.