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August 11, 2000

5 Min Read
E stands for Ergonomics in this EOAT


Manually loaded hammer handle skeletons with automatically inserted machined 
metal cores wait for the robot at the assembly station in Goshen Rubber's 
multimachine manufacturing cell (far left). The robot deposits the reusable cores 
retrieved from downstream in the top tier of the rotary station (center), and then 
descends to remove the core/skeleton assemblies for further overmolding (right). 

You may have recently read in the trades of an award-winning dead-blow hammer from Emerson Tool (see May 2000 IMM, p. 202). Sold at The Home Depot under the Ridgid brand name, the hammer features an ergonomic handle flawlessly molded of two materials in three steps (see photo below). Though there was a lot of news in the initial reports about what the handle was made from, there was little on how it was made. IMM went to find out. 

At the Englewood, OH plant belonging to the handle's molder, Goshen Rubber, IMM finds a highly automated manufacturing cell with a robot transferring subassemblies from station to station, while simultaneously handling reusable machined-metal core inserts, used to both facilitate robot handling and ensure overmolding position accuracy. The cell consists of three small presses, two of which are serviced by a multitasking servo robot with an end-of-arm tool (EOAT) as ergonomically designed to fit the production process as the finished hammer is designed to fit a human EOAT. 

Here's how it works (follow above from left to right):
Press #1: Left- and right-handed handle skeletons are molded with a reddish-orange Montell Hivalloy PP in a two-cavity cold runner mold. Handle overmolding involves use of six two-cavity cold runner tools: three for right-handed hammer handles, and three for left. The skeletons are appropriately boxed for use on demand. Mattec production monitoring systems keep track of everything. 

Press #2: Skeletons are manually loaded onto a two-tiered, rotary-table assembly station. The reusable cores are pneumatically inserted into the skeletons. The robot removes core/skeleton assemblies from one tier, after positioning reusable cores retrieved downstream into the other tier for assembly. The core/ skeleton assemblies are then positioned by the robot for overmolding ergonomic and stylish details into the hammer handle with AES Santoprene 8000 TPE in a color blended to match the reddish-orange PP skeletons. The overmolded TPE detailing covers the molded-in letters that identify the skeletons as being right- or left-handed. Maguire blenders are used throughout. 

Press #3: The overmolded skeleton/cores are then positioned in the third press and are overmolded again, this time with a gray Santoprene 8000 TPE. The extremely tight tool tolerancing and robot alignment of the skeleton ensure precise sealoff between the different colors. Also, the words "Right" and "Left" are molded into the base of the handles here. The cores then are hydraulically pulled. Finished parts fall onto a Dyna-Con parts conveyor underneath the press clamps, as the robot removes the cores for transfer to upstream assembly. Battenfeld Gloucester granulators recycle any scrap. Final assembly of the hammer and handle takes place at Emerson. 

Robotic Ergonomics
Alfred Dassler, project manager of Goshen Rubber's Thermoplastics Div., attributes the success of this complicated cell to the cooperative activities of all the parties involved, not the least of which is Eagle Mold Co. of Carlisle, OH. Eagle Mold designed and built all seven of the molds for the project. The cell cost ,000, minus the tooling. One month after the project started in October 1998, Dassler says Eagle Mold started cutting production tooling. Dimensions were taken directly from shared CAD files. 


The Ridgid hammer features an ergonomic
handle molded of two materials in three steps. 

Battenfeld, intimately involved since day one, choreographed all of the cell automation and supplied the machinery, including three 88-ton Model BA 800 CDC molding machines, and the company's Model R-10 servo robot. A 33-tonner nearby also runs vibration-dampening plugs used in the final assembly. Dassler makes special mention of the contribution of Trent Fisher, general manager of SAS Automation. SAS, also in the loop from the project's onset, designed and built the custom EOAT that makes the entire cell work. 

Goshen Rubber's Alfred Dassler (right) worked closely with his suppliers, like Trent P. Fisher of EOAT specialist SAS Automation, to design the multimolding cell. Fisher was called on to supply a custom-built EOAT with two sets of independently acting grippers capable of handling right- and left-handed hammer handles. 

SAS designed a two-by-two, all-aluminum, all-pneumatic EOAT with a total of four part nests. The top and bottom sets of grippers are designed to work independently and to handle both left- and right-handed handles. Fisher explains that the 45-durometer TPE was too soft for positive gripper contact and required alignment accuracies. This prompted collaborative work between SAS and Eagle Mold, resulting in, among other improvements, a redesign of the core inserts that allows the robot to grasp pins at the tops of the metal cores, rather then the handles themselves. 

Looking back, Goshen Rubber's Dassler says the project went quite well. "Sure, we definitely had our share of hiccups and bloody noses," he says, "but we learned what can be done when you work closely together with people that you can count on." 

Contact information
Goshen Rubber Cos., Thermoplastics Div.
Palmer Plant
Englewood, OH
Alfred Dassler
Phone: (937) 836-3303, ext. 117
Fax: (937) 832-1727

SAS Automation Ltd.
Xenia, OH
Trent P. Fisher
Phone: (937) 372-5255
Fax: (937) 372-5555
Web: www.sasgripper.com
E-mail: [email protected] 

Eagle Mold Co.
Carlisle, OH
Wilbur Wisecup
Phone: (513) 746-3331
Fax: (513) 746-3332

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