Weld fixturing from virtual to reality

When Neil Porter, founder of NCAD Products Inc., added his first initial to CAD (computer-aided design), he created a name that spoke to the very "CAD-centricity" of his new company.

Located in Oviedo, Fla., a suburb of Orlando, NCAD Products is a manufacturing job shop founded in 1996.

 "I started the company by moonlighting CAD services.  Besides CAD, I also have a background in fluid power, pneumatics, and project management. These disciplines taught me the value of scrutinizing every job to figure out how to maximize the application of technology—by which I mean CAD and CNC capabilities—to production of every project," Porter explained.

The strategy of driving operations from this digital perspective makes NCAD extremely competitive.  As a result, the company has grown into a 15,000-sq.-ft. facility, encompassing everything from 3-D-modeling and 3-D-laser scanning, used for reverse engineering and digital enlargement of models, to 5-axis foam sculpting, multiaxis milling and routing, CNC press brake forming, vacuum forming, and all types of finishing. 

First-time customers typically come to NCAD for overflow.  But the range of capabilities the NCAD team offers is such that it is not unusual for a customer to return at a later date for additional services. 

Tale of a Tail

In November 2007 a manufacturer of military simulation and training devices, also located in Florida, asked NCAD to propose an approach using 3-D laser scanning of the tail section of a non-airworthy UH-60 Blackhawk helicopter (see Figure 1). The 3-D scans were to be used to generate 3-D models required for the manufacture of full-scale, remove-and-replace simulators. The Army used these simulators for maintenance training on Blackhawk tail systems and components.

Ultimately, NCAD's laser scanning technology was not selected; however, the evaluation process led the simulator manufacturer's project management team to visit NCAD's facilities.

At that time the manufacturer was seeking to broaden its roster of fabricators. Based on a demonstration of NCAD's capabilities, the simulator manufacturer decided to place a multifaceted job with NCAD for turnkey fabrication of Blackhawk stabalator mock-ups. Stabalators are small, horizontal stabilizing winglets, approximately 34 by 72 in. long, one each located on both sides at the rear of the tail boom.  Project scope included the right- and left-hand winglets (mirror images), as well as the center actuator box, which mechanically controls the winglets' angle of attack, to which they are attached.  Besides requiring dimensional accuracy, the winglets had to be within ± 10 percent of actual weight.  All in all, this project proved to be the perfect challenge for NCAD's integration capabilities.

NCAD's design called for machined metal components and a square-tube weldment to be sandwiched within CNC-cut foam.  The resulting assembly was then to be sheathed in plastic.  Finally, vacuum-formed plastic elements were to be added externally, and the whole assembly painted.  With the exception of welding, all work was to be completed in-house.

Bring in the Welding

NCAD had planned to outsource welding until the customer proposed an expanded assignment. While NCAD was still in the initial stages of machining the stabalator components, the customer returned to ask if NCAD would be interested in producing the entire Blackhawk tail pylon mock-up. The pylon frame substructure was to be a weldment  approximately 14 ft. tall, made of 2- by 2-in. 6063 aluminum square tube (see Figure 2).  It was to be skinned in T-52 sheet. Machined parts were specified as 6061 aluminum. The catch was they wanted it completed in 90 days. The simulator manufacturer knew that at that time NCAD did not offer in-house welding, but was also aware of Porter's extensive welding and fabrication experience.

Previous NCAD projects had resulted in relationships with skilled, local welders, one of whom Porter hired.  Additionally, Porter purchased a Lincoln variable-frequency power supply.  The right approach to fixturing, however, remained unclear.

 "We are a SolidWorks house and wanted to leverage the performance of welding fixturing via intelligent use of CAD.  The idea was to optimize welding setups and add value to the Blackhawk project now, while positioning us to recoup our fixturing investment on future jobs.  But what kind of fixturing could do that?" Porter said.

He discussed this reasoning with his welding supply house, which put him on to the Demmeler modular fixturing system from Bluco Corp., Naperville, Ill.

CAD-friendly Modular Fixturing

According to Porter, the Bluco system offered two key benefits, making the decision to bring welding in-house easier.

"The system is modular and reusable, eliminating the cost of nonrecurring fixturing. And it's set up in SolidWorks—our preferred modeling platform—enabling us to define the fixture and the completed weldment before the job even hits the floor."

Fixturing is developed virtually by bringing together 3-D models of the finished weldment within 3-D models of the fixturing (see Figure 3).  Fixturing models are developed utilizing tools Bluco provides.  The precision of the fixture elements provides datum points that facilitate determination of design issues or shortcomings, in either the weldment or fixturing models before real metal is committed. This reduces mistakes, material costs, and wasted time and motion.

NCAD acquired two 40- by 40-in. tables that serve as platforms on which to mount the angles, blocks, and other fixturing accessories that are included in the standard 125-piece kit. It also purchased two extra-large, adjustable angles. Bluco assisted with the first fixturing design at no additional cost.

The tables are made of 1-in.-thick high-tensile-strength steel, ribbed to ensure stability.  Tables have 1.1-in.-diameter mounting holes on a 4-in. grid across the face and four sides of the table with an accuracy of ± 0.001 in. hole to hole and  ± 0.002 in. overall.  Fixture elements match the holes and grid pattern on the table.  Structural pieces have 1.1-in. slots to position fixtures between holes.  Positioning and clamping bolts attach fixtures and workpiece positioners.

Clamping bolts insert through the fixturing elements and the worktable.  An O-ring in the body of the bolt helps prevent rotation during tightening.  Turning the knurled bolt head extends a series of five locking balls into a chamfered recess at the bottom of the mounting holes to center the bolt shank and clamp the components together.  With each element positioned, a hex wrench tightens the bolts.

The stability, hardness (nitrided to Rockwell 55C), and flatness (0.004 in.) of the table make it efficient to use in conjunction with metrology instruments, such as a height gauge.  In addition, the table has a scribed millimeter scale. 

"The system will make reorders simple. Weldments can be fixtured at any time by calling up the 3-D model for exact duplication.  Again, no wasted time and motion," Porter remarked.