Automating the Dispensing Process
December 31, 1969 |Estimated reading time: 6 minutes
Manual, time/pressure and automated dispensing systems all have their appropriate places within the manufacturing support spectrum; the evolution of one system to the other follows a logical progression.
By Marc Cortez
Dispensing technologies are advancing as rapidly as other sectors in support of manufacturing processes, and currently offer end-users systems that only recently have become available. However, before discussing the criteria for evaluating the automated version and the applications best suited for it, a brief discussion of the various types of dispensing is in order.
Manual DispensingThe low end of the materials dispensing process is the manual form. Its basic components are extremely simple: a solution to be dispensed, typically adhesives, sealants or lubricants, and some form of applicator. A typical manual system includes a dispensing barrel and stopper filled with a material. Another might include a barrel and a dispensing gun. While component sophistication varies, many characteristics of manual dispensing are common.
Figure 1. The TPD system delivers a measured air pressure from 1 to 100 psi for a specific time via an adjustable regulator and gauge.
Manual dispensing is perfectly suitable for low-volume/accuracy/repeatability applications where product yields of 70 to 80 percent are acceptable. In operations that produce less than one million units per year and where dispense repeatability of greater than 10 percent is acceptable, manual dispensing is a viable and economical fluid-delivery process. On the other hand, low product throughput and yield are significant limitations of manual systems. Although a typical operator can dispense material for approximately 4,000 units per day, dispensing accuracy is inconsistent since operators must control both the time and pressure characteristics of the dispensing cycle. This process variability can result in higher reject rates or lower product yields vs. those of this process's alternatives.
Time/Pressure Dispensing (TPD)TPD is the next step in the process's evolutionary cycle and it eliminates many manual dispensing inaccuracies. Generally, TPD adds a regulated pressure control and timing circuit on top of the manual dispensing components to provide a means to increase product throughput and yields. Because dispensing accuracy is highly affected by pressure and timing, adding regulation to these variables significantly increases a system's accuracy.
A typical TPD system is shown in Figure 1. In operation, the electronic controller delivers a measured air pressure for a measured time span to a disposable syringe barrel or other time/pressure valve. The latter may be a pinch tube, needle, mini-spool or spray filled with a fluid material. This controlled shot of air forces the material out of the delivery end of the barrel, through a dispensing tip and to the application surface. Standard dispensers control the discharges via an adjustable regulator and gauge that varies air pressure from 1 to 100 psi.
Because TPD systems are more accurate and permit tighter process control, they offer higher product yields and greater overall throughput than manual systems. Yields of greater than 95 percent are frequent while repeatability errors of less than 3 percent commonly are achievable with TPD. However, while faster, TPD systems remain limited by operator constraints and do not provide the means to increase throughput beyond certain volumes. Applications that require higher throughput must look for other, more advanced dispensing alternatives.
Automated DispensingAutomated dispensing systems are the next technological step and offer options ranging from simple X-Y axis movement to sophisticated, autonomous, vision-controlled robotic operation. There are two main characteristics of an automated dispensing system: time/pressure regulation (temporal control) and motion or spatial control. Automated dispensing systems combine the tight dispensing control of TPD with the head-placement accuracy of stepper- and servo-motor controls, resulting in highly accurate, repeatable and reliable dispensing processes.
Figure 2 shows an industry-standard X-Y-Z table system. A microprocessor-driven controller regulates time and pressure while the gantry arms are controlled by precision servo motors. The dispensing program is developed and managed by a Windows-driven software development environment and can be used (or modified) as often as needed.
Reasons for AutomatingReasons for automating a dispensing process generally relate both to increased productivity and product quality. For example, the automated system shown in Figure 1 is capable of dispensing fluids on 3,600 parts per hour, or approximately one each second. This is contrasted with manual dispensing rates of 500 parts per hour and an immediate throughput increase of 720 percent. Such a productivity increase is significant and provides an almost immediate return on capital investment.
Other, and perhaps more important, reasons for automating a dispensing process relate to improved product quality. By increasing dispensing accuracy, overall product yields likewise are increased due to lower material waste, rework costs and reject rates. Depending on production volume and assembly expense, the cost savings because of higher product quality can be significant.
Additional cost savings with automation may be realized from greater assembly line flexibility (faster changeover), decreased downtime and lower setup costs.
Evaluation Factors to ConsiderThe first step in considering process automation is to completely understand the dispensing process's requirements and how it is used in product assembly. Some key questions include:
· What material must be dispensed?
· What volumes are to be dispensed and at what (exact) sites?
· What is the dispensing pattern?
· What are the human (limiting) factors? Can they be "engineered" out?
· Do the parts lend themselves to palletization, i.e., organized for easy and repeatable dispensing?
Figure 2. An automated X-Y-Z (bench) dispensing system's time/pressure operation is microprocessor-driven while the gantry is controlled by precision servos.
The better the understanding of these dispensing requirements, the better the analysis for determining whether the process can be automated. In cases where the exact dispensing parameters are not well understood, manufacturers are urged to contact their automated equipment supplier for a more detailed analysis of the dispensing process.
The second major factor in considering automation is the cost analysis. Some major points include:
· What is the cost of the automated dispensing machine?
· What are the production/labor rates for operating the machine?
· What are current product yields and how much can be saved by increasing them?
· How many more parts can be made (increased throughput) and how much incremental revenue will each part generate?
Other less tangible considerations include the perceived market value of increased product quality and operator/personnel issues.
Automated Dispensing OptionsOnce the decision has been made to change from manual dispensing to a more automated operation, there are numerous options available. A first step is to remove the human time variable and install a simple time/pressure system (Figure 2).
A second step is to use a stationary dispensing station with a syringe mounted on a stand as an operator moves the part underneath. Next is to add true motion control, ranging from a simple, pneumatic up-down motion to a multi-head and multi-axis robotic dispensing table. The last step in the evolution is to add "intelligence" in the form of features such as vision sensing and true volumetric control.
The Best CandidatesWhile the factors influencing automation of a dispensing line vary by application, there are many common parameters.
Generally, those processes that require a consistent and repeatable operation on similar parts are good candidates for automation. Also, automation is best suited for medium- to high-volume applications, or processes that dispense more than one million parts per year. Parts with high per-unit cost and a high degree of value-added labor also are prime candidates for an automated dispensing machine. Additionally, parts that lend themselves to palletization those that can be mounted on a standard platform also are good automation subjects.
SummaryAs manufacturers grow and assembly processes evolve, the number of options for automating fluid dispensing systems also increases. Manual dispensing processes have inherent limitations in quality and throughput of which time/pressure systems may solve. Adding both temporal and spatial control to dispensing processes significantly increases the quality and reliability of dispensing, which equates to increased product yields and greater overall assembly line efficiency. Current technology offers manufacturers unprecedented opportunities to automate their dispensing processes efficiently, quickly and cost-effectively.
MARC CORTEZ may be contacted at Techcon Systems Inc., 12151 Monarch St., Garden Grove, CA 92841; (800) 776-0440; Fax: (714) 799-6804; Web site: www.techconsystems.com.