Part Buyers Authority Issue #2

Meeting the OEM performance criteria for these wheels is a task that requires a great deal of effort. Kentucky Chrome Works is the only US based plater certified to OEM specifications. We polish and chrome plate alloy wheels manufactured by any Tier 1. We have a “dealer direct” program wherein we take in new painted alloy wheels (with no or very low mileage and no road damage); have the paint non-chemically stripped, polish and plate the wheel to OEM specifications. Producing an OEM wheel from raw aluminum ingots to finished product involves many different stages. In simplified form, the stages are below: PRE-PLATE 1) Casting 2) Heat treatment 3) Machining PLATE 4) Polish 5) Pretreatment 6) Copper Buff 7) Plate Pre-plate operations such as casting, heat treatment, and machining can have a tremendous impact on the metal finisher. For example, poor casings can result in porosity in the plating, leading to CASS failures, poor machining may cause adhesion and cosmetic failures. Many problems that are evident after plating may have a root cause, which is outside of the plater’s control. The actual plating process for OEM wheels is divided into two fundamental operations, pretreatment and plating. Pretreatment is normally defined as all of the process steps up to the copper buff, while plating is defined as all the processes performed after the buff. So, while a nickel strike over zincated aluminum and acid copper plating are actually plating processes, they are part of the pretreatment line. Conversely, cleaning and activating the buffed copper wheels are technically pretreatment operations, but in wheel plating nomenclature they are incorporated into the plating line. The pretreatment processing chemistry and sequence utilized must be capable of processing the specific aluminum alloy used. Typically, the aluminum used for cast OEM wheels is A356. 356 aluminum comes in many varieties, with the specific type represented by the alloy designation. For example, some alloy names include a letter before the alloy number. This letter is used to identify alloys that are slightly different in alloying composition or impurity levels. Examples include A356 or A380, which are just a bit different from 356 or 380. In addition, there may be a decimal notation following the alloy. Thus, an aluminum alloy XXX may be designated as XXX.0, XXX.1 or XXX.2. The decimal indicates the following: • XXX.0 - Indicates the composition limits applied to an alloy casting. • XXX.1 - Indicates the composition limits for ingots used to make the alloy casting. • XXX.2 - Indicates the composition limits for ingots used to make the alloy casting, but which are normally tighter limits than no designation (XXX) or a designation of 1. In practical terms the XXX.1 designation generally denotes aluminum ingots from a secondary source, such as ingots recycled from scrap aluminum, while the XXX.2 ingots are primary aluminum produced from reduction cells. Pretreatment is often considered the most important step in any finishing operation, and while it is a complex science, there are several basic objectives for pretreatment operations in OEM wheel plating: • Create a clean, active, uniform surface on the aluminum substrate. • Remove foreign material from the surface of the aluminum substrate. • Modify the aluminum substrate surface to create a specific surface topography that generates mechanical bonding sites. • Prevent the highly active aluminum from forming a passive oxide layer prior to plating operations. Continued on page 24 23 Click here to SUBSCRIBE o r CONTRIBUTE a s an author.