AGMA 05FTM02-2005 pdf download.The Effects of Pre Rough Machine Processing on Dimensional Distortion During Carburizing.
The raw material selected for use in the new manufacturing cell was normalized bar stock, which was within the engineering requirements of the finished gear. The soft normalized bar stock was viewed as a good choice for machinability. Many literature sources supported this conclusion. Moll (1985) defined machinability as being related to the ease with which a material can be machined with reasonable tool life. Verzahntechnik Lorenz (1980) and Cluff (1992) indirectly used a similar definition stating that machinability (reasonable tool life) decreases as material hardness increases. The two key terms are ease of material removal” and reasonab4e tool life.” An indication of expected surface integrity is not present using these definitions of machinability.
Material hardness can be used as a machinability indicator due to the close relationship between hardness and microstructure (Mullins, 1990). However, hardness is an accurate representation of machinability only for similar microstructures. Mullins (1990) states that a tempered martensite matrix will exhibit superior machinability to a pearlite matrix of similar hardness. Woldman (1937) studied micro- structure and machinability and noted that a micro- structure selected for long tool life would not necessarily produce good surface integrity.
Based on literature and experience, a tempered martensitic microstructure was desired to produce the required surface integrity. The addition of the hardening and tempering operation was viewed as a risk to changing the dimensional distortion during carburizing and hardening.
A great amount of manufacturing development had been done implementing the new cell. The dimensional distortion during carburizing and hardening had been established and had been determined acceptable and manageable. The addition of a hardening and tempering operation prior to rough machining was viewed as an addition to cost, lead time, and risk of increased dimensional distortion during carburizing. Increased dimensional distortion would then require more process development time and cost.
Problem Statement
Common ground: Aerospace power transmission components must be manufactured to the highest quality standard while minimizing cost of nonquality.
Destabilizing condition: Gear tooth surfaces inconsistently have poor surface integrity (lears”) present after finish flank grinding. The surface detects are produced during the semi-finishing, prehardening, operation. These gears are then deviated, reworked, and/or scrapped.
Contributing factors: Aerospace gears are expensive and have long lead times. A study of many vanables is not always practical using actual gears.
Problem: The shaping machine used in the manufacturing cell has limited cutting parameters. Literature suggests that hardening and tempering the material prior to any machining will improve the surface integrity during shaping. The material structure is then martensitic and hardness ranges from Rc 25 to Rc 32. However, literature also suggests that this fix could negatively influence dimensional distortion during hardening.
Solution: Material samples made of different micro- structure and hardness will be fabricated and tested. Paired data studies statistically analyzing dimensional distortion will be performed on coupons of similar size and process.
Assumptions
The material samples are assumed to fully represent their population. For example. a group of normalized material samp’es is assumed to represent all normalized material.
The change in coupon gap width is assumed to represent the relative dimensional distortion of an actual gear.
Methods & Procedures
This section contains the details of coupon manufacturing and processing. Standard distortion coupons were manufactured for each population as shown in Figure 2. The dimensions of the coupon are proportional to the gear being developed and are shown in Figure 3.AGMA 05FTM02 pdf download.