Why Do Draw Dies Fail? by: David M. Rascati Vice President Sales Premier Wire Die 1712 Dividend Street Fort Wayne, IN 46808 USA www.premierwiredie.com — “Memory Joggers” Wire, Rod & Bar Dies was less wall thickness of the insert to counter the pressure of the incoming rod. There is a grey area in understanding and selecting the proper insert for each type of material. This die design may have worked for drawing copper or aluminum, but since it was stainless steel, it failed. Size wasn’t the only problem. The insert was sent to a lab to find out the grade of material. We wanted to make sure the die had the proper grade for the application. Too hard of a grade of carbide could have allowed the die to crack. The lab’s response was that they couldn’t be definitive about the grade, because the sample was too porous. The lab tech stated that the carbide was either “under-sintered or under-pressed”, which in this case he believed it to be under-sintered. Poorly sintered carbide doesn’t allow for the matrix of tungsten and cobalt (or nickel) binder to mesh properly, thereby allowing weakness in the integrity of the part (reference Figure 1 and Figure 2 , courtesy of General Carbide ). Figure 1 is of poorly sintered carbide that is likely under-There have been many articles written by industry experts such as Dr. Roger Wright , Dr. Horace Pops and Tom Max-well that have focused on die design and wire drawing theory, but very little has been written on why draw dies fail. Why not? Draw dies are the heart of the operation and their success or failure is tied to manufacturing performance and costs. A broken or poorly designed die is worse than no die at all if it is producing scrap! The paper on which this article is based was written to enlighten the reader on how material flow, lubrication and tooling interact and contribute to a myriad of production failures, and more importantly, what to look for when draw dies fail. The following case studies include issues with raw ma-terials , die construction , draw stock , mechanical failure , lubrication and die design . So why do draw dies fail? Why do Draw Dies Fail? Poor Quality Raw Materials Underneath every quality carbide tool is a quality Preform. Preforms are semi-formed parts made of sintered carbide powder that die companies use for making draw tooling. Die companies depend on the quality of the preform as they grind and polish the rough outer surface of the tool. A poor quality preform means wasted time and resources in finishing. Die companies take a loss when the preform requires extra work to polish it. Customers take a loss when the tool fails in production! One of the first things they teach you in the carbide in -dustry is how critical the sintering process is to the quality of the carbide. Sintering is the process that transforms pressed carbide powder into a solid piece. Time, temperature and pressure are all important parameters that must be carefully controlled during this process. The parameters for sintering are based on the grade of material and size of the part. For example, a small R2 and large R16 inserts of different grades may have to be sintered in different processes. An inadequate sintering process may lead to various metallurgical defects such as porosity, grain growth and eta-phase. An engineer at a large rod mill provided a competitor’s experimental die that broke prematurely. She believed it broke because they were taking too heavy of a draft. I believed that it was likely a tool design issue. In this particular case, the insert had a major circumferal crack about 1/3 of the way down the approach angle. While evaluating the incoming and the exit rod diameters, I realized the insert was too small for the draft. In order to accommodate the incoming rod size through the smaller insert, the die company used a wider angle. Going with a wider angle compromised the integrity of the insert as there 94 Wire & Cable Technology International/November 2017 Fig. 1 — Poorly sintered carbide that is likely under-sintered. Fig. 2 — Properly sintered and etched carbide.