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Sequential valve gating: ultimate control for the toughest molding jobs.



Parts consolidation in automotive and other applications is creating larger parts with more complex geometries. These parts tend to be harder to fill and susceptible to problems of overpacking, warpage, and flashing. At the same time, these large, complex parts have to meet stricter surface-quality requirements. Demand is also rising for family molds of different-sized parts, for parts that combine different materials, and for greater flow lengths in thin-wall parts.

Conventional valve-gated hot-runner systems are having a tough time handling these challenges. Opening and closing all the valve gates at the same time necessarily limits the degree of control over weld or knit lines, gas traps, localized packing, and unbalanced flow. Fortunately, there is a technique that provides almost unlimited control over which parts of a tool fill when and how fast. It's called sequential valve gating, or SVG (Scalable Vector Graphics) A vector graphics format from the W3C for the Web that is expressed in XML. Introduced in 2001, SVG was designed to become the standard vector format just as GIFs and JPEGs have become the standard bitmaps for the Web. . Adding a programmed time sequence to the opening and closing of valve gates is not new technology, but molders are gradually gaining appreciation of its problem-solving prowess.

Take, for example, family tools that have a complex geometry in one cavity and simple dimensions in another, or a multi-gated part that is asymmetrical or has thick and thin areas or ribs, bosses, or living hinges. "These circumstances can invite problems during molding," warns Bruce Casey, general manager of Plastic Engineering & Technical Services (P.E.T.S.), a supplier of hot-runner systems. In such cases, molders with conventional valve-gate systems may have to overpack some areas of the part in order to completely fill out other areas. These overpacked areas not only waste material but are also vulnerable to problems of sticking, warpage, and frozen-in stresses, adds Ken Kurtz, hot-runner product manager for D-M-E.

In subsequent painting operations, part stresses can create problems with splay or paint adhesion. Further more, the overpacking could demand the use of a more robust press with a larger injection unit and increased clamping requirements.

Simultaneous filling from multiple gates can also be a problem with other decorative processes such as in-mold lamination lamination

a laminar structure or arrangement.
 (or back molding). Textiles or films inserted in the tool may fold or ripple if the filling process is unbalanced.

For multi-gated single-cavity parts, the position and appearance of weld lines is becoming increasingly important. Occurrence of a weld line in a critical high-stress area can compromise the integrity and performance of the part, says John Blundy, Incoe's v.p. of business development. Multiple gates can also produce weld lines that remain visible even after painting.

"A knit line in a colored part will result in glaring visual-effect problems, while a knit through a glass-filled part would have a negative effect on both the aesthetics and the performance," agrees Kurt Weiss, manager of part performance and new material introductions at GE Plastics.

Many solutions have been tried, including the costly one of controlling fill by adding sliders sliders

a species of tortoise kept as pets. They have a black shell and a red stripe behind the eye. Called also Chrysemys scripta elegans, red-eared sliders.
 to the mold, Kurtz notes. "Some molders may have tried to control the fill pattern by restricting nozzle bores and gates in order to reduce overpacking, stress, or weldline issues, but that can lead to excessive melt shear at that smaller orifice orifice /or·i·fice/ (or´i-fis)
1. the entrance or outlet of any body cavity.

2. any opening or meatus.orific´ial


aortic orifice
," says Harald Schmidt Harald Franz Schmidt (born August 18 1957 in Neu-Ulm, Germany) is a German actor, writer, comedian and television entertainer best known as host of two popular german late-night shows. , president of Mold HotRunner Solutions (MHS (1) (Message Handling Service) An earlier messaging system from Novell that supported multiple operating systems and other messaging protocols, including SMTP, SNADS and X.400. It used the SMF-71 messaging format. ). "This idea may be good when molding the same part with the same wall thickness, but bore balancing locks you into a narrow processing window for other jobs," he adds. "You cannot change the viscosity of the material, the pressures, or the temperature. With SVG, the molder gains control over the cavity fill pattern to produce quality parts even when the material or the conditions change."

A somewhat better approach may be to adjust runner sizes rather than gate sizes to shift weld-line locations, says Murali Annareddy, product line manager at Moldflow, the mold-simulation software provider. "This method of artificially balancing the flow is quite popular with family molds. Moldflow provides an automatic flow-balancing program that sizes the runners. However, this might result in differing amounts of shear experienced by the melt, which could affect part quality." Freeze-off is another risk in the smaller runners, Annareddy warns. "And an artificially balanced feed system is typically more sensitive to changes in the process settings."

In the past, difficulties such as these forced some molders to rule out the use of multiple gates or more than a few cavities in high-precision applications because uniform, tight part tolerances were simply too hard to achieve.

What SVG brings

After 10 years of commercial availability, SVG is gaining favor as an alternative to traditional valve gating and thermal gating methods. Some of the delay may be due to the long lead times for automotive projects. But SVG is proving its unprecedented ability to control knit lines, which can be moved to a non-critical area, or even out to a vent. Sequencing of the valves also provides a way to fill family molds uniformly and to eliminate overpacking and flashing. Similarly, a bad cavity in a multi-cavity mold can be blocked off without throwing the whole tool out of balance. "A molder can achieve balanced fill using the gates instead of through runner and manifold sizing," says Neil Dewar Neil Hamilton Dewar (born November 11, 1908 in Lochgilphead, Argyllshire - ??? ) was a Scottish footballer who played as a forward.

Dewar began his professional career at Third Lanark in 1929 and scored 124 goals over four seasons, helping them to the Second Division title
, product engineer at Mold-Masters.

Suppliers cite other benefits, too: Progressive fill through a few gates at a time can reduce clamp-tonnage requirements by 20% to 30% as compared with filling through all gates at once. Pack and hold can be profiled with greater precision, supplying longer or more intense packing to just those areas that need it.

At least eight suppliers of hot-runner technology offer SVG technology. They include D-M-E, Incoe, Husky, MHS, Mold-Masters, Osco Systems, P.E.T.S., and Synventive. These firms say they have installed from dozens to hundreds of SVG systems.

Automotive is the major market focus for SVG, especially for large parts like bumpers, fenders, wheel liners, rocker panels, grilles, fans, radiators, air-intake systems and instrument panels. Optical parts like lenses are also a target. SVG is also opening the doors for valve gating in leading-edge automotive applications like in-mold lamination, film-insert decorating, coinjection, hard-soft multi-material molding, gas assist, and long-glass composites. Mark Moss, Synventive's senior v.p. of sales, marketing, and R&D, cites one example: "Coinjection of TPO (Twisted Pair Only) Refers to the use of twisted pair wire when other options are available. For example, a TPO suffix at the end of 3com Ethernet adapter model numbers indicates the card has only an RJ45 connector.  automotive bumpers is not a big market right now, but it is being run successfully." Sequentially molding a TPO bumper with a virgin skin and recycled core could help auto makers meet coming requirements for "green" vehicles. A part like that wouldn't be moldable with a standard valve-gate system, according to according to
prep.
1. As stated or indicated by; on the authority of: according to historians.

2. In keeping with: according to instructions.

3.
 Moss.

Incoe also worked on SVG for coinjection three to four years ago with Bemis Manufacturing Co., Sheboygan Falls Sheboygan Falls may refer to:
  • Sheboygan Falls, Wisconsin
  • Sheboygan Falls (town), Wisconsin
, Wis. Coinjection was used to capture a dissimilar material in the core.

Automotive molders have a big cost incentive to get away from painting. Suppliers believe SVG will be important to the growth of decorative film insert molding as a replacement for painted exterior parts such as door panels.

Osco Systems, which claims to have invented the SVG technique, first applied it to solving cosmetic problems in auto parts Auto parts are components of automobiles. They mainly are, in alphabetic order (only car specific articles or articles with car section):
  • Air filter
  • Automobile self starter
  • Bell housing
  • Brakes
  • Bucket seat
  • Bumper
  • Buzzer
  • Battery
. "At least 10 years ago, we worked on dozens of molds for truck and car grilles for GM and encountered knit-line problems. We used SVG to move the lines from plain sight out to a bezel The front cover of a desktop or tower computer case. The term also refers to the individual drive bay covers, which are removed to install CD-ROMs and other removable drives that require access from the front of the case. ," says Osco sales v.p. Peter Rebholz. "About the same time, we started to work with in-mold decoration, where SVG could roll the plastic into the mold and not degrade TO DEGRADE, DEGRADING. To, sink or lower a person in the estimation of the public.
     2. As a man's character is of great importance to him, and it is his interest to retain the good opinion of all mankind, when he is a witness, he cannot be compelled to disclose
 or blow over the insert applique. We also started using SVG with family molds, making a packaging lid and container in one mold," says Rebholz.

"We've seen SVG applications going back 10 to 15 years for items such as back housings for televisions. It allowed the molder to produce acceptable large parts that didn't need painting," says Mold-Masters' Dewar. "We've also seen applications done with 30% glass-filled nylon for an automotive under-hood application. Weld lines would have deformed de·formed
adj.
Distorted in form.
 the part surface and affected the part from a structural point of view."

Collins & Aikman of Troy, Mich., is using SVG for a challenging in-mold lamination project, says Mark Nietzke, program manager for interior trim development. 'The SVG system is employed to control the filling pattern in the tool and also to help lower the pressure that the foambacked vinyl insert would see in the injection phase." The 16 x 20 in. polypropylene part is produced with an SVG system from P.E.T.S. in a joint venture with molder Engineered Plastics Products of Owasso, Mich. Previously, these parts were injection molded and then hand wrapped with the foam/vinyl covering. Nietzke says Collins & Aikman will shortly launch another SVG project, this one a vinyl-covered door panel for GM's Epsilon 1. (language) EPSILON - A macro language with high level features including strings and lists, developed by A.P. Ershov at Novosibirsk in 1967. EPSILON was used to implement ALGOL 68 on the M-220.  car. Three of four molds for the project are already built and being validated for the process. An SVG fabric-covered instrument panel is being considered for the model 2006-07 year, he adds. Collins & Aikman also has in development an SVG seat back for Visteon.

One of the most high profile SVG parts is a two-component weather strip for the Ford F150 pickup truck. The first shot is a 20% talc-filled PP. The second shot, produced in a rotating mold on one machine, is a soft Santoprene TPV TPV Temporary Protection Visa (Australia)
TPV Terminal Punto Venta
TPV Third-Party Verification
TPV Thermophotovoltaic
TPV Thermoplastic Vulcanizate (thermoplastic elastomer)
TPV Total Payment Volume
 with a silicone additive for lubrication lubrication, introduction of a substance between the contact surfaces of moving parts to reduce friction and to dissipate heat. A lubricant may be oil, grease, graphite, or any substance—gas, liquid, semisolid, or solid—that permits free action of . Innatech of Rochester, Mich., a custom injection molder specializing in multi-shot operations, expects to mold up to 1.4 million of these parts per year. The thin, 38-in.-long weather strip, which goes between the front and rear side doors is a combination sound damper damp·er  
n.
1. One that deadens, restrains, or depresses: Rain put a damper on our picnic plans.

2. An adjustable plate, as in the flue of a furnace or stove, for controlling the draft.
, weather seal, and cosmetic closeout closeout, closure

the finalization of a feeding program in a feedlot. The cattle are sold and a balance sheet is struck which includes the costs of feeding and housing or confining them.
, says Jack Elder
For the Australian rules football umpire, see Jack Elder (umpire).


Jack Arnold Elder (3 July 1949 - ) is a former New Zealand politician. He was an MP from 1984 to 1999, representing first the Labour Party, then New Zealand First, and then Mauri
, advanced development manager. SVG is used only on the TPV edge seal. Five gates are used to fill gradually from the center in order to erase gate blemishes, knit lines, and gas traps, says Elder. All gates are set at angles of 30[degrees] to 45[degrees] to avoid gate blemishes. The SVG system comes from Incoe, but Innatech designed its own PLC control system for the process. This system allows discrete on/off control of each valve gate multiple times within the injection cycle, based on a screw-position signal from the press. The part was a finalist in this year's SPE SPE - Software Practice and Experience  Automotive Plastics Innovation Awards.

Cosmetic enhancement is a major reason for using SVG, but not the only one. Husky has used SVG to reduce clamp tonnage by nearly 30% on a 1500-mm-long fascia fascia (făsh`ēə), fibrous tissue network located between the skin and the underlying structure of muscle and bone. Fascia is composed of two layers, a superficial layer and a deep layer.  impact absorber, reports product manager Kevin Golden. "Our components are used to do a lot of automotive grilles. Most large-nozzle systems are being done with SVG." Husky has built SVG systems for parts weighing as much as 80 lb.

As far back as 1995, Nascote Industries, Nashville, Ill., a leading large-part automotive processor and early adapter of SVG, dropped cycle time from 110 sec to under 75 sec to mold a bumper from GE's Xenoy PC/polyester resin. Most of the savings came from reduced clamp-force requirements. The firm also said faster cycles with SVG allowed it to increase capacity without additional presses. It also provided relief from splay and paint-adhesion problems.

MHS and German partner MHT MHT Multiple-Hypothesis Tracking
MHT Male Hose Thread
MHT Mental Health Team
MHT Multiple Hypothesis Testing
MHT Manchester, NH, USA - Manchester (Airport Code)
MHT Multi-server Hyper-threading Transportation
 recently cooperated in building several large automotive SVG hot halves with 6000-lb plates for Decoma's plant in Germany. MHS's Schmidt sees SVG opening the door to multi-cavity tools for large thin-wall parts. "In the future we will see TPO bumper fascias with 2-mm wall thickness or less," he says. "The thinner wall will contribute to a shorter cooling time (Law) such a lapse of time as ought, taking all the circumstances of the case in view, to produce a subsiding of passion previously provoked.
- Wharton.

See also: Cooling
, but this will increase the flow resistance of the melt. More severe weld lines will be due to a higher pressure drop and a faster cold-layer formation. But SVG prevents these problems in large thin-wall parts."

There are plenty of non-automotive markets for SVG, too. "We've done sequentially gated parts that fit in the palm of your hand," says Osco's Rebholz. GE Plastics developed a notebook computer A laptop computer that weighs in a range from five to seven pounds. The term originated when laptops were routinely more than 10 pounds, and those that became lighter were placed in a special "notebook" category. In practice, notebook computer and laptop computer are synonymous.  case with only a 1-mm wall that was filled sequentially through 11 gates. "We wanted to push the envelope," says Greg Tremblay, senior process engineer. GE developed a carbon-filled conductive conductive

having the quality of readily conducting electric current.


conductive flooring
flooring or floor covering made specially conductive to electrical current, usually by the inclusion of copper wiring that is earthed
 compound of its Lexan polycarbonate A category of plastic materials used to make a myriad of products, including CDs and CD-ROMs.  that "flows like dried mud," Tremblay says. It would not fill correctly with a conventional valve-gated system. Using SVG, they were able to fill the part in less than 1.5 sec.

Several roads to SVG

The majority of SVG systems in the field typically use from four to 12 drops, but some have as few as two gates and as many as 24. Casey of P.E.T.S. says on average an SVG system costs about 15% to 20% more than a standard valve-gate system, mainly for the extra control capability.

SVG can be divided into two main applications that have somewhat different mold-filling aims. One SVG approach is suited to multi-cavity molds like family tools. It seeks to achieve balanced filling without overpacking. The other is so-called "cascade" molding, which is generally applied to long or large parts for improving part finish, says D-M-E's Bob Starr, manager of marketing services.

Cascade molding is designed to emulate the single melt-flow front and lack of weld lines obtained when only one gate is used. A cascade design positions the gates so that the melt flow length from one nozzle ends just past the gate of the next nozzle. When the melt passes a nozzle, that nozzle is opened. The new melt comes in behind the preceding flow front. Hot melt from the new nozzle "rejuvenates" the melt front ahead without forming a weld line.

The cascade can be designed to flow from the center of part out to both sides or from one end of a part to the other. A third approach may be to open the gates on both outer part edges and bring the two melt streams together at the center of the part. In either case, "the objective is to keep the melt flow moving before it sets up," says Osco's Rebholz. Setting different temperatures at each gate tip may assist in this goal.

The distance the melt front travels from one gate to another and the timing of opening and closing gates are critical parameters in SVG. "If you open the second gate too early you will get backflow backflow /back·flow/ (-flo) reflux or regurgitation (1).

pyelovenous backflow  drainage from the renal pelvis into the venous system occurring under certain conditions of back pressure.
 and all sorts of nasty consequences," warns Innatech's Elder. "If you open the gate too late, the material from the first gate will be solidified at the surface. In either case you won't reap the benefits of sequential valve gating." Backflow can occur because the material approaching the second gate is cooling and losing pressure, while material fresh from the new gate is hot and under more pressure.

Gate opening can be triggered by time, screw position, or a pressure transducer Pressure transducer

An instrument component which detects a fluid pressure and produces an electrical, mechanical, or pneumatic signal related to the pressure.
 in the cavity. Proximity switches that provide feedback on the valve gate's pin position can be useful as a safety check.

Proper venting is always important in SVG, advises Casey of P.E.T.S. "If the mold is not vented properly, air between two melt flows can be trapped in the tool."

Due to the number of complexities involved in SVG, many hot-runner suppliers advocate use of computer flow simulation when designing the mold. Moldflow has been involved in SVG simulation for several years. Weld lines are a particular focus for users of SVG flow simulation. "There is currently no way for simulation to predict the actual strength of the weld, so the best one can do is look at the predicted temperature and pressure at which the weld line is created. In general, weld lines created at high temperatures and pressures will be stronger. We can then time the opening and closing of the gate to minimize or eliminate those weld lines," says Moldflow's Annareddy.

Even SVG may not provide adequate local control of filling and packing pressure in large, complex parts. In such cases, Synventive says its Dynamic Feed SVG technology picks up where standard SVG leaves off. Unlike typical valve gates, which are either fully open or fully closed, DF nozzles can be opened or closed to varying degrees, changing the effective size of the flow orifice. DF thus provides real-time filling and packing control at each individual gate. "What Dynamic Feed amounts to is a dimmer switch dimmer dimmer switch n (Elec) → Dimmer m;
(US) (Aut) → Abblendschalter m 
," says Synventive's Moss.

Introduced as far back as 1998, the closed-loop DF system has a hydraulic cylinder Hydraulic cylinders (also called linear hydraulic motors) are mechanical actuators that are used to give a linear force through a linear stroke. Operation
Hydraulic cylinders get their power from pressurized hydraulic fluid, which is typically oil.
 that moves a special flow-control pin in the nozzle. A pressure transducer in the hot runner A hot runner is an injection mold component containing a series of channels that distributes molten plastic within a mold to increase molding productivity through reduced waste, as the runners arent wasted each cycle by being ejected, as the plasic stays molten and gets used on the  sends a signal to the controller, which compares the actual pressure to a set pressure profile. The controller operates a servo An electromechanical device that uses feedback to provide precise starts and stops for such functions as the motors on a tape drive or the moving of an access arm on a disk.  valve that controls the movements of the hydraulic cylinder. Whereas conventional injection molding injection molding
n.
A manufacturing process for forming objects, as of plastic or metal, by heating the molding material to a fluid state and injecting it into a mold.
 uses velocity control during the filling stage and then switches over to pressure control for final filling and packing, DF uses pressure control only. DF is said to provide the most accurate control over packing, since pressure is sensed right at the gate.

Says Moldflow's Annareddy, "With this control, you are no longer restricted to ensuring that all the cavities fill at the same time." Moldflow and Synventive are working together on DF mold simulation.

Tier-one automotive supplier Lear Corp., Southfield, Mich., has used DF to make numerous interior A-, B-, and C-pillars as well as HVAC (Heating Ventilation Air Conditioning) In the home or small office with a handful of computers, HVAC is more for human comfort than the machines. In large datacenters, a humidity-free room with a steady, cool temperature is essential for the trouble-free  doors, bumpers, wheel-arc liners, and a three-part overmolded cluster bezel. Other molders have used DF to mold interlocking interlocking /in·ter·lock·ing/ (-lok´ing) closely joined, as by hooks or dovetails; locking into one another.
interlocking Obstetrics A rare complication of vaginal delivery of twins; the 1st
 bracket supports, precision ink-jet cartridges, and stud sensor assemblies. One thin-wall, multi-cavity project produces mobile-phone front and back covers in a four-gate mold. Mikron mi·kron
n.
Variant of micron.
 Mould Technology in Faareveje, Denmark, produces the PC/ABS PC/ABS Polycarbonate/Acrylonitrile Butadiene Styrene  parts with an injection time of 0.4 sec. The housings have a wall thickness from 0.7 to 1.5 mm. Total cycle time is 13 sec for the parts, which require a shot weight of 8.85 g.

While not revealing details, P.E.T.S. is planning to roll out a new valve-pin design for SVG during the first quarter of 2004 that "does more than open or close all of the way when actuated ac·tu·ate  
tr.v. ac·tu·at·ed, ac·tu·at·ing, ac·tu·ates
1. To put into motion or action; activate: electrical relays that actuate the elevator's movements.

2.
," says Casey.

NEED TO KNOW MORE?

D-M-E Co., Madison Heights Madison Heights, city (1990 pop. 32,196), Oakland co., SE Mich., a suburb of Detroit; inc. 1955. With the decline of the regional auto industry, the city has become a technology center for companies from a number of industries. , Mich. (248) 398-6000, www.dme.net

Incoe Corp., Troy, Mich. (248) 616-0220, www.incoe.com

Husky Injection Molding Systems Ltd Husky Injection Moulding Systems Ltd was founded by Robert Schad, a German immigrant who came to Canada in 1951 with $25 borrowed from an uncle and a letter from a family friend by the name of Albert Einstein. ., Bolton, Ont. (905) 951-5000, www.husky.ca

Moldflow Corp., Wayland, Mass. (508) 358-5848, www.moldflow.com

Mold Hotrunner Solutions Inc., Georgetown, Ont. (905) 873-1954, www.moldhotrunnersolutions.com

Mold-Masters Ltd., Georgetown, Ont. (905) 873-2818, www.moldmasters.com

Osco Inc., Rochester Hills, Mich. (248) 852-7310, www.oscosystems.com

Plastics Engineering & Technical Services Inc. (P.E.T.S.), Auburn Hills, Mich. (248) 373-0800, www.petsinc.net

Synventive Molding Systems Inc., Peabody, Mass. (978) 750-8065, www.synventivs.com
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Author:Knights, Mikell
Publication:Plastics Technology
Article Type:Cover Story
Date:Dec 1, 2003
Words:3079
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